On Monday, the January transfer window drew to a close without Arsenal bringing in a left-back - despite loaning Sead Kolasinac out to FC Schalke 04 last month.As a result, Arsenal are low on full-time senior left-backs. There’s the injured Kieran Tierney, but the only real alternatives to the Scottish international are Cedric Soares and Bukayo Saka. Neither of them would consider left-back to be their best position.The obvious next question is whether Arsenal have any promising left-backs in their academy setup. Let’s take a look at the possible options for promotion.Joel LopezFor me, Lopez is the top candidate to step up. The 18-year-old joined Arsenal from Barcelona in 2018, slowly progressing through the ranks to make his u23 debut in February 2020.Lopez then became an u23 starter this season. Recently, he has been training with the first team from time to time.The teenager is having an impressive campaign, although it’s been disrupted by injuries. He missed the first month of football with a problem he'd picked up in 2019/20, and he suffered a couple more knocks towards the end of the year.Unfortunately, that’s part of the reason he hasn’t made a first-team squad appearance already. His best opportunity would’ve been in the latter stages of the Europa League group stage, but that’s when he was ruled out of action.Nonetheless, the young Spaniard is a good prospect. He’s dangerous going forward, making strong runs and causing the opposition problems with his crossing. He also makes good recovery runs and tackles, though he’s far from perfect defensively at this stage in his career. I absolutely believe he will make his Arsenal debut at some point, it’s just about when.The biggest problem for Lopez is his lack of senior experience. He’s never played a senior game, nor featured in a senior squad, not even for a friendly. It might be hard to find a way in right now, with little room to experiment while every result is so vital.Tolaji BolaLike Lopez, Bola has never made an appearance for the Arsenal first team. Unlike Lopez, he does have some senior experience, spending the first half of this season on loan with Rochdale in League One. He also made a single appearance in a competitive Arsenal squad when Unai Emery picked him for the bench against Nottingham Forest in 2019.Bola has played over 50 times for the Arsenal u23s, and he was their starting left-back at the beginning of the current campaign. He provided a nice assist against Ipswich Town in the EFL Trophy and was subsequently linked with a loan move away.The 22-year-old joined Rochdale, where he initially made regular appearances, before dropping to the bench in December.The problem for Bola is that he’s been passed over in the past, even when Arsenal were desperate for a left-back. They’ve consistently chosen to give other players chances out of position - even players younger than Bola - rather than calling him up.Advert InsertedIt just doesn’t seem like he’s really in contention for opportunities, and an uninspiring loan spell won’t have done particularly much to put him ahead of the alternatives.Ryan Alebiosu19-year-old Alebiosu is having an encouraging season with the u23s so far, appearing to grow and develop with each game he plays. Personally, I used to think he was a bit too lanky and easily pushed off the ball before this season, but he’s looked like a different prospect with some strong displays recently.Mostly, he’s played right-back, but he’s also spent a few games on the left. His last game at left-back was a 2-1 win over Leicester City in December in which he assisted the winning goal. He was involved in every big chance the team had in the second half.I’d say the biggest factor counting against Alebiosu is that he’s a right-footed player who usually starts on the right. There’s no real advantage to picking him over Cedric Soares, unlike with Bola or Lopez, who can more naturally hug the touchline. He’s also another one without any senior experience.Ben CottrellCottrell is not a left-back, he’s a central midfielder. He often plays in the number 10 role, but also works well as a number eight. When he came on for his senior competitive debut against Dundalk in December, he replaced Emile Smith Rowe, not Ainsley Maitland-Niles (who was playing left-wing-back on the day). I’ve never seen him play at left-back at youth level.Having said that, he’s often mentioned among the possible left-back options for two reasons. Firstly, he’s left-footed. Secondly, he came on at left-wing-back in the senior friendly match against MK Dons in pre-season.In a way, his skillset is well-suited to a wing-back role. He’s on the smaller side, but that allows him to be agile and work well in tight spaces. He’s a creative player who could easily make chances from the left, and he has a tenacity about his work off the ball that Arteta would surely love.It’s just impossible to recommend him for the role of backup left-back/wing-back when I’ve never even seen him play the position, outside of those 28 minutes against MK Dons in a friendly.Final ThoughtsThere’s no perfect candidate to step up, with each option clearly having drawbacks. The only one with any experience in the Arsenal first team (Cottrell) isn’t really a left-back, the only one to play regular senior football this season (Bola) was subsequently dropped and recalled from his loan. It’s not ideal.My feeling is that we won’t see any of the four starting for Arsenal at left-back before the end of the season. It's not about talent or potential, just inexperience. But that can change. A couple of injuries or some really impressive performances in training, and you never know.