Fulham boss Marco Silva admits Joao Palhinha may've dislocated his shoulder.
The midfielder suffered the injury in their preseason friendly against Brentford in Philadelphia.
"Unfortunately it doesn't look good," Fulham boss Silva said.
"He's probably dislocated his shoulder. Tomorrow he is going to do a scan and it will be more clear. Let's hope it's not another long-term injury for us."
Fulham ran out 3-2 winners on Sunday.