The opening of a new transfer window always brings with it a sense of promise, the problems from the previous season will be resolved with new signings and squad improvement - but it's worth remembering that it doesn't always work out that way.
During his 21 years in charge of Arsenal Football Club, Arsene Wenger has had his fair share of buys that didn't work out. For every Thierry Henry, there's been a Francis Jeffers, for every Laurent Koscielny, a Seb Squillaci.

Below is Arsene Wenger's Worst Signings XI:

GOALKEEPER: Richard Wright
DEFENDERS: Mikael Silvestre, Sebastian Squillaci, Phillipe Senderos, Andre Santos
MIDFIELDERS: Kim Kallstrom, Andrey Arshavin, Julio Baptista
FORWARDS: Park Chu-Young, Marouane Chamakh, Francis Jeffers

Richard Wright
When Wright signed for Arsenal in 2001, the 23 year-old was seen as David Seaman's successor at both club and country level. He had a successful time at Ipswich City, making 240 appearances, and had just broken into the English international fold, being brought along to Euro 2000. Things did not work out as planned for the goalkeeper, however.
Making 22 appearance for Arsenal throughout the 2001-02 season, Wright did not capitalise upon a run in the team following an injury to Seaman and slipped to 3rd choice, mainly playing FA cups (which incidentally, Arsenal won, with Seaman replacing Wright in the final).
Wright retired last year, having a long career playing for top clubs - without actually featuring that often (including a hugely successful 4-year spell at Manchester City between 2012-2016 where he didn't make a competitive appearance).

Mikael Silvestre
In August 2008, Mikael Silvestre ended a decorated 10-year spell with Manchester United and made the move to the Gunners. Perhaps if the signing had taken place just a few years previous, it would have represented a good signing.
But there was a reason United did not need him anymore and allowed him to transfer to a league rival. Silvestre was passed it.
The French defender was a far cry from the player who had won Premier League titles in Manchester. He was a liability when he played and once his two-year contract was finished, his time in north London was over. He played in Germany, India at America following his exit, before retiring in 2014.

Sebastian Squillaci
If Squillaci's £3.2m signing in the Summer of 2010 has even went reasonably well, it could have represented a bargain buy from Wenger.
On paper, Seville's 30-year-old defender had exactly what was needed at the time – an experienced centre back, who'd give his all and even had international experience. Unfortunately, Squillaci's time at Arsenal started mediocrely and only got worse.
Replacing the aforementioned Silvestre, Squillaci didn't even have that much to live up to. But it became evident quickly he was a dud, at times seemingly lacking basic defensive attributes and the ability to read the game.
Squillaci is still plying his trade at Bastia in Ligue 1, now 36.

Phillipe Senderos
After a promising start in an Arsenal shirt, young Swiss defender Phillipe Senderos career with the Gunner's wasn't spectacular.
7 years in north London seen Senderos play 64 times for Wenger's side, and seen him go on 2 loan spells (the first Everton, the second Milan). While he perhaps wasn't as bad as others on this list, he was found out defensively too frequently and was overly reckless by times.
He went onto play for a number of other clubs in England, such as Fulham and Aston Villa, and has recently been released at 32-years-old by Rangers.

Andre Santos
In 2011, Arsenal needed to make a number of signings to bolster the squad following the departures of Samir Nasri and Cesc Fabregas. One of these signings was Andre Santos.
Arriving with a respectable reputation on deadline day in 2011, the 28-year-old had amassed 22 caps for his country Brazil. Costing £7m, perhaps the full-backs greatest flaw was that he wasn't a great full back.
Santos wore the number 11 shirt for Arsenal, which was apt, considering he spent the majority of his time away from the defence.
Santos most infamous came against Manchester United in the November of 2012, when he swapped shirts with Arsenal's recently departed former captain Robin Van Persie at half time, following a particularly disheartening performance. Suffice to say, that didn't go down well.
Santos was loaned to Gremio in February 2013 and is still playing at 34, having played for a number of clubs since - most recently Boluspor in Turkey.

Kim Kallstrom
One of the strangest signings throughout Wenger's reign, Kim Kallstrom signed on loan for Arsenal during the January transfer window of 2014, to stay till the end of the season.
During the 31-year-old Swedish midfielders medical, it was discovered that he had a back injury (rumours suggesting it was picked up attempting an ambitious bicycle kick on a beach in Dubai were never confirmed). Arsenal decided to still sign him so he could begin his rehabilitation, making him the ONLY signing of this window.
Kallstrom didn't recover till late March, where he made a 10-minute sub appearance in the Premier League. His next appearance would be the week after, where he was introduced as an extra-time substitute in an FA Cup semi-final against current Champions Wigan Athletic – where he actually scored a penalty in a victorious 4-2 shootout.
Although he only made 4 appearances for Arsenal, Kallstrom said he enjoyed his time at the club. The sheer peculiarity of the signing earns him a place in this XI.

Andrey Arshavin
After signing for Arsenal for a club record fee from Zenit St. Petersburg and being one of the shining lights of Euro 2008, Andrey Arshavin became the clubs first big signing since moving to the Emirates.
During his first year with the Gunners, he was runner-up for player of the year, and bagged FOUR goals against Liverpool at Anfield, one of the greatest performances by any player in the Premier League era. So how did it all go wrong?
By the time he was released, fans were glad to see the back of Arshavin. Perhaps Wenger was playing him out of position, or perhaps he was genuinely lazy but things didn't go as well as it looks like they could have for the Russian. Still playing for Kairat in Kazakhstan at 36 after another spell in Russia.

Julio Baptista
In 2006, "The Beast", Julio Baptista finally made his way to London after being linked with Arsenal for years, coming on a season long loan from Real Madrid.
His notable physicality was thought to be the answer to Arsenal's lack of strength in midfield, but sadly it wasn't enough, and he was shipped back to Madrid after 24 appearances, in which he scored 3 goals. He continued to have successful career, recently retiring after a season I the MLS with Orlando.
He did however, in the same vein as Arshavin, memorably score 4 goals at Anfield against Liverpool in a 6-3 League Cup win.

Park-Chu Young
Another transfer from August 2011, Young apparently left his medical for Lille in France to board a flight to London to sign for Arsenal on deadline day.
If Young's last-minute signing had worked out, it would be the stuff of lore - Wenger pulling off another coo on-par with Vieira coming to north London 15 years previous. It sadly didn't pan out that way.
When the 26-year-old South Korean forward made his Premier League debut against Manchester United in January 2012, he surely wouldn't have thought that it would be the only competitive appearance he would make for Arsenal during a 3-year spell with the club. That is however, how it played out. After a set of loans, Chu-Young was released in June 2014.
He's now rebuilding his career in South Korea, playing for FC Seoul.

Marouane Chamakh
When Moroccan striker Marouane Chamakh made the move from Bordeaux to Arsenal in 2010 on a free transfer, his career in a red shirt got off to a promising start.
11 goals in 22 appearances in all competitions had Arsenal fans ready to begin believing they had finally signed the striker they had been looking for. This made Chamakh's decline even more difficult.
Scoring 4 in his next 46 games, by the end of his tenure, Chamakh's confidence was shot and he was making little or no impact when he played. He was released in 2013.
Now 33, he has since played for West Ham, Crystal Palace and Cardiff City.

Francis Jeffers
Francis Jeffers was a young English striker that came to Arsenal following a big money £10m move from Everton in 2001. His goal-poaching style wasn't (or indeed isn't) the kind of striker that Wenger usually opts for, and fans had been hoping for a "fox in the box".
Sadly, Jeffers genuine potential was never realised at Arsenal, and injuries dogged his time at the club. He only made 22 appearances and scored 4 goals over 3 years before being loaned back to Everton in 2003, where after a large amount of clubs, he's made his way back too and is now an academy coach after retiring in 2013.
To this day, he impressively still holds the joint record (tied with Alan Shearer) for most goals for the English Under-21's, scoring 13.