Willian has warned that Chelsea will likely miss out on top-four finish if they do not improve on the current form.
The winger is concerned about Chelsea's poor form following Tuesday's 2-2 draw with 10-men Arsenal at Stamford Bridge.
Tuesday's outcome means Chelsea have now dropped 18 points at Stamford Bridge from a possible 36, and Willian has expressed serious concern.
"I think we have to be careful," he told The Mirror.
"If we don't then maybe at the end of the season we will be out of the top four. We have time, we have a five-point gap, so now it is time to improve.
"I don't know if it is concentration. We have to see what we can improve. We have to improve at home, and we have to be more stable, win more games.
"To stay in the top four we have to win games, so now is the time to see which part of the game we have to improve."
Chelsea remain six points clear of fifth-placed Manchester United, though the Old Trafford club has a game in hand.
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