Christian Pulisic scored the opening goal but was substituted before the start of the second half during Chelsea’s 5-2 defeat against West Brom on Saturday.
Pulisic, who has been plagued by injuries since joining the Blues, had started a league game for only the second time since Thomas Tuchel’s arrival at Stamford Bridge.
Tuchel intended for him to remain on the pitch after half-time but Pulisic did not feel he should continue.
He was therefore replaced by Mason Mount.
Boss Tuchel explained: “Christian did a sprint when he came back out for the second half and said he felt his hamstring would not survive the game if he continued, so we made the decision to substitute him.”