James Morrison came on in his place and scored from the penalty spot.
"I'm not sure. I've not really had a chat with the doctor," Clarke is reported to have said about Amalfitano's injury on Goal.com.
"He was indicating that he had an injury. We tried to get him to half-time but he said it was too bad, so we made the change.
"We'll assess him and see what the problem is."
West Brom's defeat to Liverpool means they are 12th in the Premier League.