Chelsea may already be regretting one of their decisions in the summer transfer window.

The Blues had the opportunity to strengthen their defence with an established Premier League centre-back, but ultimately decided against making a move.

At the time, Chelsea had other priorities and had already been linked with several defenders. However, with Maxence Lacroix now facing a lengthy spell on the sidelines, the decision is beginning to look rather questionable.

And one recent performance has only added to the frustration.

Chelsea may regret Ilya Zabarnyi decision

According to reports in the summer, including one from talkSPORT's Alex Crook, Chelsea were offered the opportunity to sign Ilya Zabarnyi during the transfer window but turned it down.

The Ukraine international had only joined Paris Saint-Germain from Bournemouth for £57million 12 months earlier, but was reportedly open to leaving after spending much of the Champions League campaign on the bench.

Instead, Alonso's side signed Lacroix just days later. Despite early criticism, that decision has not been a bad one, but the Frenchman's hamstring injury has changed things.

Lacroix is expected to miss around two months, leaving Wesley Fofana and Levi Colwill as Alonso's main centre-back options. There is very little room for another injury before the manager is forced to consider alternative solutions.

Zabarnyi, meanwhile, has been showing exactly what Chelsea could have added to their squad.

His performance against Le Havre on Friday was a particularly impressive one. The 24-year-old completed 90 of his 95 passes, made six clearances, two interceptions and six recoveries. Most impressively, won three duels and wasn't dribbled past.

Of course, one performance does not tell the whole story, but those numbers prove the quality he could have brought to Stamford Bridge. He also already had Premier League experience from his time at Bournemouth.

Chelsea could regret not adding more defensive depth

Chelsea have spent years being criticised for having too many players, but the pendulum may have swung too far in the opposite direction.

Alonso's squad looks particularly vulnerable in certain positions, and centre-back is becoming an obvious concern.

Lacroix's injury is an unfortunate setback rather than something the club could have predicted. However, Chelsea knew they were taking a risk by not adding another experienced option when the opportunity came knocking.

Zabarnyi would have provided competition, cover and valuable experience in English football. He might not have been guaranteed a starting place, but that isn't the point. A club hoping to qualify for multiple competitions needs more than two main centre-backs.

Chelsea cannot go back and change their summer business, but they may have to address the consequences in January.