Chelsea are facing a dilemma with right-back Reece James after he pulled out of training due to a knee problem.
The 21-year-old had a scan on his knee at Chelsea's training ground on Sunday morning which reveaed that he has a fluid build-up in his joint.
The club is now weighing up the best course of action, though the injury is understood not to be too severe.
James initially suffered the injury following a collision with Daniel Podence in Chelsea's 2-1 defeat at Wolves on Tuesday. The England international trained with his club on Friday before complaining that his pain was increasing.
Chelsea now face a decision on whether to wait for the problem to settle or try to accelerate the recovery through a minor operation.
James will likely miss Monday's match against West Ham, with Cesar Azpilicueta set to step in at right-back having lost his place to James despite being the club captain.
Meanwhile, Blues head coach Frank Lampard is expecting to welcome back both Callum Hudson-Odoi and Hakim Ziyech, who trained for the first time on Friday ahead of the London derby.
Hudson-Odoi, in particular, is confident that he can be ready for at least a bench role to help his side who have lost their last two games away at both Wolves and Everton.
The absence of a host of wingers in recent weeks has been a struggle for Lampard's side to overcome.
Christian Pulisic had a spell on the sidelines with a persistent hamstring problem that he first sustained in the FA Cup final defeat to Arsenal in August. That was coupled with injuries to both Hudson-Odoi and Ziyech in the last few weeks.
Kai Havertz also received a positive Covid-19 test and was said to have suffered particularly bad symptoms, which has disrupted his match sharpness.
Chelsea will be happy to have most of their squad available ahead of a busy period. After the West Ham match they have two games in two days with a trip to Arsenal followed by a home clash with Aston Villa.
Lampard and Chelsea had called for the number of substitutes allowed per match to be increased from three to five to help ease the pressure on Premier League squads.
However, the option was voted down for a third time having been used previously during Project Restart when the league continued after the first UK lockdown due to coronavirus. Lampard spoke of his frustration at the decision ahead of his clash with the Hammers.
"When we spoke about it as managers, the overriding factor from managers, whether they were maybe for or against, was that this is a case of player welfare, making sure we are looking after players and giving them the best opportunity to play at optimum level and not putting them at risk and such, because of the uncertain times and the schedule," Lampard told reporters over Zoom.
"And that schedule gets tougher, for instance we play two games in three days over Christmas. So I think it would have been really beneficial for player welfare. Normally the modern-day player welfare comes out on top, I don't think it quite has this time.
"But the decision's been made, and we carry on."