Manchester United loanee Dean Henderson could be facing a spell on the sidelines.
The English keeper, on loan at Nottingham Forest, suffered what appeared to be a muscle injury during a 2-0 win over Leicester City on Saturday.
Henderson did finish the game after suffering the issue late in the game, but seemed uncomfortable at the final whistle.
Forest manager Cooper told reporters post-game: "My first impression is, not good.
"But scans will tell more, with more clarity in the next day or two. We will have to see how that goes.
"It's a muscle injury, I think it's his thigh, but I'm not sure."