Chelsea manager Antonio Conte has revealed that Gary Cahill was treated in hospital for a small stone in his kidney this week.
The 31-year-old has emerged as a doubt for this weekend's FA Cup semi-final against Tottenham Hotspur at Wembley having only been released from hospital on Thursday.
Conte insists that the problem is not a serious one, but admitted that his on-field captain is likely to miss Saturday's showdown with Spurs.
"He arrived at the training ground with a bit of fever. Our doctor preferred to bring him to the hospital and to check his condition," the Italian told reporters.
"Not a serious problem, but now Gary is getting better and is improving a lot. If you ask me for tomorrow, my answer is it is very difficult. This period is not a lucky period for us."
Cahill has been an ever-present for Chelsea in the Premier League this season, starting all 32 of their matches.