Chelsea will be without midfielder N’Golo Kante for Tuesday’s Champions League group game at AC Milan.
Kante, 31, has not travelled to Italy after suffering a reaction to an existing hamstring injury in training.
The French World Cup winner has not played since the 2-2 Premier League draw with Tottenham on 14 August.
“It’s disappointing for him and us, but we have to wait and see the extent of it, and go from there,” said boss Graham Potter.
Morocco winger Hakim Ziyech will also be missing for Chelsea at the San Siro through illness.
Red Bull Salzburg currently lead Group E on five points, with Chelsea and Milan, who they beat 3-0 in the reverse fixture in second and third on four points.
