Chelsea goalkeeper Petr Cech will miss Sunday's Barclays Premier League clash with Everton after a scan today revealed he has a small tear in his calf.
The Czech Republic international limped out of last night's Champions League game against Schalke 04 at half-time after sustaining the injury in mysterious circumstances early on.
Club doctor Bryan English told the club's official website, www.chelseafc.com: "It's still early but it's almost certain he will miss the game this weekend.
"We will also be liaising with the Czech FA's medical department about Petr's injury. Hopefully the international break will allow time for the injury to improve."
Cech added: "I don't know exactly how it happened.
"I only know that I felt a pain from the 10th minute of the match. Nevertheless I played the first half.
"I feel bad that I will be out right now when myself as well as my team are both doing well."
Frank Lampard defended Chelsea's poor Champions League performance against the German side by insisting it is difficult to be "pretty" all the time.
The Blues were lucky to escape with a goalless draw against the Bundesliga side they had defeated 2-0 at Stamford Bridge a fortnight ago.
Schalke hit the woodwork twice in the second half, while Chelsea's Didier Drogba squandered three gilt-edged chances to provide the visitors with another perfect European away day.
The German side halted Chelsea's run of seven straight wins under new coach Avram Grant but stand-in skipper Lampard was typically forthright about the outcome of a game which keeps the Blues on top of Group B.
Lampard admitted: "We were not at our best and Schalke had chances, especially at the end, to win. So we have to be happy with a draw.
"I think it says something about our resilience and there was a bit of luck as well. We didn't play particularly well and you need that at times.
"You have to come away and dig in sometimes. These are the sort of things that make a good team and all teams need a bit of luck and resilience.
"You cannot be pretty all the time and sometimes you have to dig in.
"We have won seven on the spin and you cannot keep playing better and better. We didn't last night but hopefully it is the result which will help us to qualify if we win our next game.
"It can be difficult and a long process with a busy league campaign in between where we have been trying to claw ourselves back into the title race.
"There are certain games where it gets difficult and you have to remember the goal is to finish top of the group and qualify.
"It is expecting too much for everything to be perfect straight away, and I don't think anyone is perfect anyway.
"Whichever team you go to, I have seen Manchester United, Arsenal and Liverpool travel in Europe and have the occasional very tough game.
"If you come out with a draw, sometimes you are very happy and that is us.
"It might be a good part of the learning curve, a reminder to us that after seven wins we needed a slice of lucky to get a draw and need to make sure in the next game we get back on a winning streak.
"It took a big effort to go on the run we were on but we are used to that.
"We are used to long, heavy seasons and have to be mentally strong.
"The manager thing has been and gone now and there are no excuses there. We have to look forward and I think the team was pretty fresh at Schalke."
