Roberto Martinez confirmed he expects to be without Muhamed Besic and Kevin Mirallas for Wednesday's Capital One Cup semi-final second leg against Manchester City.
The Blues travel to the Etihad with a 2-1 advantage, but won't be able to call upon Besic and Mirallas for the trip after the pair limped off with hamstring and knee injuries respectively in the 2-1 defeat to Swansea City.
"It's hard to tell [the seriousness of both injuries]." he explained after the game. "Muhamed Besic injured his left hamstring - the opposite leg to the problem he had recently.
"We will also assess Kevin Mirallas, who injured the tendon in his right leg around the knee.
"I don't expect them to be fit for Wednesday and I expect a bit of a period where they will be unavailable. It is a real shame because both players gave us a really refreshing look and reached good levels at this stage of the season."
Martinez also explained that Phil Jagielka, who recently returned from a knee injury that kept him out for more than two months, was rested with a busy schedule in mind.
"We have five games in 13 days," he added. "Phil Jagielka has been out for a long, long time and then he came back last week and played three games in seven days.
"Medically, it was the right thing to give him a bit of recovery time and make sure we used the squad. The squad is ready to cope with players missing and, clearly, Phil Jagielka will be refreshed for what is ahead."