Chelsea centre back Antonio Rudiger was dismissed early from a training session on Sunday after he clashed with goalkeeper Kepa Arrizabalaga, the Telegraph reported.
The report said the pair squared up to each other after Rudiger went in late on the goalkeeper and that they had to be separated by team mates. The defender was then sent to the changing room five minutes before the end of the session.
Reuters has requested comment from Chelsea, who suffered a shock 5-2 defeat by second-from-bottom West Bromwich Albion on Saturday that ended their 14-game unbeaten run in all competitions under Thomas Tuchel.
Christian Pulisic was taken off before the start of the second half due to concerns about his hamstring but Tuchel hoped that by catching the problem early they may have prevented a more serious injury.
"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 ... We had to make the decision to substitute him straight away," Tuchel told reporters.
"I hope it's not a bad injury but just a little problem."
Pulisic was making only his second start under Tuchel and scored the opening goal before the 22-year-old American was replaced by Mason Mount.
Midfielder N'Golo Kante is also nursing a hamstring injury sustained on international duty with France.
Chelsea are fourth in the league with 51 points from 30 games. They face Porto in the first leg of their Champions League quarter-final on Wednesday.