Thomas Tuchel faces difficult decision with Chelsea's true undroppable unable to face West Ham

For the third successive home game, Thomas Tuchel walked into the small media room at Stamford Bridge and delivered a post-match press conference full of frustration, irritation and exasperation. The Chelsea head coach made no attempt to hide his emotions.

"We thought we learned our lesson from Brentford and Real Madrid, but obviously not," Tuchel said after his side's 4-2 defeat to Arsenal. "The players have to face the reality that it's impossible to win matches if you make this amount of mistakes – and mistakes of this calibre. It's simply impossible. I haven't seen it in any other matches, but I see it now in consecutive matches of our games, and it has to stop."

Chelsea will have an opportunity to put things right on Sunday against West Ham United. It's another London derby against a side pushing hard for a top-four finish in the Premier League. The Blues will not have it easy as they attempt to end a disappointing run of results at Stamford Bridge.

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Tuchel will not be able to call upon his most influential midfielder, either. Mateo Kovacic suffered an ankle injury in the FA Cup semi-final win over Crystal Palace on Sunday, and the Chelsea head coach was downbeat on the Croatian's chances of featuring in the imminent future.

"It's a ligament injury," Tuchel explained ahead of the defeat to Arsenal. "Hopefully, [he will] not be longer than two weeks out, but this is a long time for us in terms of games. Hopefully, as short as possible."

At the start of the campaign, an injury to Kovacic wouldn't have caused huge alarm. Chelsea had Jorginho and N'Golo Kante in the form of their careers, while Ruben Loftus-Cheek and Saul