Chelsea boss Guus Hiddink said it was too early to speculate on the knee injury of Kurt Zouma.
The promising defender landed awkwardly and required a stretcher to leave the pitch in the second half of Sunday's 1-1 draw with Manchester United at Stamford Bridge and Hiddink is fearing the worst.
However, the Dutchman could not determine how long Zouma would be sidelined for as the club has to further assess the extent of the damage.
"The rest of the season is hopefully too much (for Zouma to be ruled out for), but he will have an examination, so I can't speculate about that," he said.
"If you've seen the images, and the experience of the hyper-extension of the knee joint, then we'll wait. It's very bad, when you land with a hyper-extended knee, a hyper-extended leg. We'll see what happens. Hopefully they have a good explanation. There are several scenarios when it's like that.
"We are unbeaten (since my appointment), but as I said before, if you want to get into fourth place, you must have victories. Considering that, we've had too many draws to get fourth place. It's difficult.
"I haven't calculated mathematically if it's possible, but we must start winning games."