Chelsea manager, Thomas Tuchel, has said Mateo Kovacic could be out for a long time.
Kovacic was missing as the Blues lost 1-0 to FC Porto on Tuesday night in the Champions League.
The Croatian trained on Monday evening, but he pulled up during the session.
Tuchel already had doubts over N’Golo Kante’s fitness and ideally did not want to risk the Frenchman against the Portuguese giants.
However, Kante was selected to start as Tuchel confirmed Kovacic sustained an injury in training, leaving him as a doubt for this weekend’s FA Cup semi-final against Manchester City.
“We had a light injury unfortunately in training yesterday which was very sad so Kova is out.
“The same with Andreas Christensen. We did not manage to make him fully fit after his muscle issues from the first leg.
“These are our two concerns, but we have Thiago back in the squad. There are not too many changes because we are on a good run and the team feels confident,” Tuchel said.