Chelsea defender Kalidou Koulibaly is a major doubt for this week's Champions League tie against Red Bull Salzburg.
The Senegalese, who joined this summer from Napoli, missed Saturday's clash with Manchester United and looks set to be absent again after missing Monday's open training session.
It is a blow for Graham Potter's side, who will qualify this week should they win in Austria.
Chelsea, already shorn of N'Golo Kante and Reece James for the foreseeable future, will be hoping the knee injury is nothing serious entering into a hectic period ahead of the World Cup in November.