John Terry has been ruled out for three weeks after injuring a muscle in his backside.
Chelsea captain Terry played for the Under-23 team against Southampton on Monday and came off 70 minutes into a 3-2 win.
Antonio Conte was unsure whether he had damaged the muscle during the game or in training the next day.
A three-week absence rules Terry out of games against Tottenham, Manchester City and West Bromwich Albion and will leave him short of match practice as the busy festive period of fixtures approaches.