Christian Pulisic picked up a hamstring problem during Chelsea's 5-2 defeat to West Brom, it has been confirmed.
The 22-year-old, who put Chelsea ahead with a finish from close range in the second, was brought off at half-time for Mason Mount by Thomas Tuchel and it raised question marks over the decision to take the American off. He had been one of Chelsea's better players.
But Tuchel has confirmed post-match that Pulisic tweaked his hamstring and asked to come off.
As reported by NBC Sports, they claim that Timo Werner was meant to come off at half-time but Pulisic sprinted five yards onto the pitch and felt his hamstring.
He went over to the Blues bench to tell Tuchel and asked to be substituted.
Chelsea will be hoping the injury is nothing serious and that the American will be fit for selection to face FC Porto next week in the Champions League.
"There was nothing much in it until the red card came and after that we were not able to cope with the situation," said Tuchel post-match.
"I don’t know why but it was like this. We gave away two very easy goals before half-time but even in the second half what could go wrong went wrong. We have to accept a big loss today and hopefully it’s a big wake-up call for all of us, me included.
"We will get the right response because this is sport and it’s absolutely necessary. First of all, it’s important that we digest it because I did not see it coming so now we have to take our responsibilities, and shake it off and continue tomorrow."