Christian Pulisic took to social media after he was forced off at half-time during Chelsea's 5-2 defeat to West Brom in the Premier League.
The 22-year-old was brought back into the starting eleven against the Baggies and bagged the opener for the Blues as he tapped in from close range after Marcos Alonso's free-kick came off the post.
But Chelsea went into half-time down to 10 men after Thiago Silva was sent off and were 2-1 down after conceding two stoppage time goals.
As Chelsea were coming out for the second-half, Pulisic emerged from the tunnel and sprinted onto the pitch and turned around almost instantly feeling his hamstring and had to come off, adding to Thomas Tuchel's frustrations in west London.
Pulisic will be hoping the tweak isn't serious ahead of Chelsea's match against FC Porto on Wednesday but it does make him a huge doubt.
He took to social media to express his disappointment with the Blues looking to bounce back.
He wrote: "Not our day...onto the next."
Chelsea are back in at Cobham on Sunday after Tuchel confirmed the players will be putting their performance right ahead of the midweek European clash.
Tuchel said post-match: "No there was no day off tomorrow, there might have only be an individual day off for the guys that had travelled to refresh their mind. So most of the players will be in.
"After 15 matches we can't lose our head and take away what we've done. After the moment it is the time to breath, it'll be a hard afternoon and evening.
"We had completely different plans how to start this match day but we have to accept it now. It's important to deal with it together."