Middlesbrough boss Tony Mowbray is concerned that Rhys Williams could be sidelined for the rest of the season.
The Australia international damaged ankle ligaments against Leeds United earlier this month.
Now he is set to wear a cast for around two or three weeks after which the injury will be reassessed.
"Rhys has damaged ligaments in his ankle and that's never a week or so, it's always a few weeks," said Mowbray.
"Let's hope we can see him again this season. The physios are hopeful that he could still have a part to play.
"We'll assess it as the weeks roll on. He'll have two or three weeks in a cast and then we'll assess it once he gets that off and starts running and see how bad it is.
"It's a blow but we have to keep going."
Meanwhile, Boro are boosted by the return to fitness of Morocco international Merouane Zemmama.
"He's had a difficult period with a lot of niggling injuries and a double hernia operation," said Mowbray.
"Hopefully he can impact on the team. Zemmama on his day is a special individual talent who can skip past opponents and create chances for the team, but we need him fit and at his best."