Thomas Tuchel started this transfer window with the clear intention of reinforcing his defensive options following the departures of Antonio Rudiger and Andreas Christensen.
Not only were those senior players of a quality capable of competing in the Premier League and Champions League, they also had suited Tuchel's defensive style at Stamford Bridge, with Rudiger reaching performance levels he had never attained previously in a Chelsea shirt.
The signing of Kalidou Koulibaly felt like the perfect response to losing a presence like Rudiger, with the Senegal international coming to England as one of Europe's strongest defenders over the past decade.
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Chelsea are trying to add one more before the deadline passes next Thursday in Wesley Fofana from Leicester. All the signs are that Leicester are open to a deal if Chelsea meet their high valuation, with a fourth bid expected imminently that could finally end a pretty public saga.
But there seems to be a trade-off coming in securing the services of the 21-year-old, allowing Trevoh Chalobah to leave on loan, likely to a Champions League-level club on the continent. Whilst the sudden shunning of the academy graduate by Tuchel has confused onlookers, particularly after Chalobah had enjoyed a pretty impressive breakthrough season, losing him only shortens an area that was supposed to be bolstered.
Not even taking into account the loan for Chalobah, Malang Sarr joined Rudiger and Christensen in the departure lounge, moving to Monaco on a season-long loan with a reported option to buy, which if things go according to plan, will be activated.
Another potential defensive option is Ethan Ampadu, an unused substitute at Elland Road last Sunday who looks set for his fourth stint away from Stamford Bridge, likely back to Serie A where he was with Venezia last season. Even if Fofana eventually signs, this would leave Tuchel with a thinner cast of personnel.
Koulibaly, Thiago Silva, Cesar Azpilicueta and Fofana would be the most recognised central defensive options in the back-three Tuchel currently plays. To boost the numbers, you would likely see two wingbacks used in Reece James and the recent addition Marc Cucurella. This feels like a makeshift solution and in the case of James, a needless handbrake to one of the club's most exciting creative threats.
You then throw those concerns over cover, coupled with the imminent introduction of Champions League football following Thursday evening's draw, and Tuchel will be praying his defenders make it to November unscathed. Given the number of games that have to be completed before the break for the World Cup in Qatar, injuries, suspension and fatigue may all play a factor.
The first two have already caused Tuchel issues in the opening three games, even with the comfort of free midweeks. In midfield, both Mateo Kovacic and N'Golo Kante have suffered injury setbacks, with the latter expected to be out for a month. In attack, Armando Broja missed the trip to Leeds with a knock, leaving an underperforming Kai Havertz as the only obvious option in the centre of attack.
Koulibaly's petulant second yellow card that saw him sent off in the dismal defeat to Leeds last weekend means he will miss Saturday's clash with Leicester at Stamford Bridge. Tuchel could be forced to bring Chalobah back into his plans, but it would not be a shock to see either James or Cucurella fill in alongside Silva and Azpilicueta instead.
Chelsea are set to play eight games in October, with very few midweeks in between domestic and European commitments, which could include trips to Milan, Zagreb or Salzburg in the group.
Signing Fofana is a priority but the trade-off is losing another defender in a season that is about to get more intense and could end up negatively impacting Tuchel's squad strength.
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