Fulham manager Kit Symons says star midfielder Lasse Vigen Christensen appears to have suffered a hamstring injury in the victory over Derby.
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The Danish midfielder limped off just before half time iin the clash at Craven Cottage, but the Whites went on to beat the league leaders with goals from Nikolay Bodurov and Cauley Woodrow.
Christensen, who has been one of Fulham's best players in a difficult season in the Championship, endured a spell on the sidelines with a pulled hamstring earlier in the season and only returned in January.
Symons believes Christensen has now injured his other hamstring, but hopes the injury will only keep the 20-year-old out for a short period.
"I'm hoping it's not serious and he won't be out for too long," the manager said. "He'll be assessed and we'll know more tomorrow. It looks like he's tweaked his other hamstring this time.
"He hadn't had a hamstring injury his whole career and now he's had two in a short space of time.
"He'd been in scintillating form before his last injury and he's played his way back in. But he's been frustrated because that pace and explosiveness hadn't quite come back.
"He's disappointed because he wants to play every minute of every game but he'll be fine. He'll bounce back and he's beginning to learn to manage his own body."
Star striker Hugo Rodallega missed the game with an injury he picked up in the 3-0 midweek defeat against Wolves.
The Colombian is close to a return, but Symons insists his place in the side is not guaranted after Woodrow impressed in attack against Derby.
"Cauley did very well so there's no guarantee for anyone," Symons said.
"Matt Smith will also be back. It's what we want at this club - competition for places."