Chelsea winger Eden Hazard faces missing a pivotal period of the season after limping out of the Champions League win over Paris Saint Germain at Stamford Bridge.
Hazard was replaced by Andre Schurrle after just 18 minutes against the French champions after picking up a calf problem in the warm-up on Tuesday night.
And Chelsea manager Jose Mourinho fears Hazard could miss the next couple of week, ruling him out at a critical sequence of fixtures.
"It is a calf," said Mourinho.
"After 10 minutes he was saying he cannot do it and even when muscle injuries are not serious it is normally a couple of weeks out minimum, but I have no idea of the dimension of the injury."
After the game, which saw Chelsea reach the semi-final after a 2-0 win over PSG through goals from Schurrle and Demba Ba', Hazard added: "I had already felt some pain in my calf during the warming-up. I didn't want to take a risk."
The injury almost certainly rules Hazard out of the Premier League games against Swansea City and Sunderland, while the Belgian international must be considered a doubt for the first leg of the Champions League semi-final on 22 or 23 April. Chelsea learn their opponents on Friday.
If the 23 year old's absence is extended, Hazard could miss the Premier League trip to Liverpool and the second leg of that semi-final, matches which will dictate Chelsea's hopes of ending Mourinho's first season back in west London with silverware.
Hazard has scored 16 goals this season for Chelsea and has been the driving force behind their domestic and European hopes and is among the contenders for the PFA Players' Player of the Year award.
The Blues trail Premier League leaders Liverpool by two points with five matches remaining though Mourinho has continually written off his side's hopes this season.