Christian Pulisic is a huge doubt for Thomas Tuchel's Chelsea side when they face Southampton in the Premier League.
The 22-year-old has faced several injury problems since his arrival in west London and could miss the Blues' match on the south coast on Saturday with a calf issue.
Tuchel confirmed that the American had picked up a tightness in his calf which could rule him out of the league meeting at St Mary's.
"We have some issues with the calf of Christian Pulisic, nothing big but it feels a little tight," said Tuchel on Friday in his pre-match press conference.
"It is nothing too serious but there is some risk of soreness there and so there is a big question mark over him at the moment."
Tuchel added: "It is our job to bring the best out of him. It is a challenge now to hold his level, to improve and maintain it. We are not worried or concerned, the medical department is on that.
"He stopped training yesterday [Thursday], I would not say it is an injury, it is just risk management that relies on his history. The main thing for Christian is to stay positive."