Chelsea manager Antonio Conte has revealed Gary Cahill is set to miss Saturday's FA Cup semi-final against Tottenham after being treated for a small stone in his kidney.
Cahill was admitted to hospital on Tuesday after training and the England centre-back had tests and treatment before being released on Thursday.
With the Premier League leaders due to play their London rivals at Wembley this weekend, Conte fears it is too soon for the England international to return to action.
"He arrived at the training ground with a bit of fever," Conte told reporters on Friday.
"Our doctor preferred to bring him to the hospital and to check his condition.
"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."
Tottenham are four points behind the Blues at the Premier League summit with six games remaining after Chelsea's loss at Manchester United last Sunday.
Although Tottenham manager Mauricio Pochettino insists his side will be underdogs on Saturday, Conte tried to put some pressure back on the north Londoners by claiming it's time for them to shed their underdog status.
"Tottenham now is a really great power in English football," Conte said.
"There is a moment you have to finish considering yourself an underdog. I think this is the right moment.
"This is the third year for them (under Pochettino).
"Tottenham is a great team. They're showing for the second consecutive year to fight for the title."