Brentford top scorer Bryan Mbeumo will be ruled out for a number of weeks due to a "bad" ankle injury picked up in the Bees' 2-1 loss to Brighton.
"It is bad. He'll have a scan later, but we don't know the exact number of weeks he will be out," Brentford manager Thomas Frank said.
"He will definitely not play on Saturday [against Sheffield United]."
The injury could put the Cameroon international's preparation for the African Cup of Nations at risk, with the tournament due to begin on 13 January next year. Cameroon's opening game is on 15 January against Guinea.