Middlesbrough have lost midfielder Julio Arca for two weeks.
The Argentine, who has been converted into a central midfielder from left-back this season, has been one of Boro's best performers.
However, he will now be missing until April.
"I have had a scan which showed a little tear in the groin," said Arca.
"I will be out for a couple of weeks.
"Maybe I will be able to play in the next match at West Ham but I think it is more likely to be Watford after that.
"I am lucky that we have a weekend off this week because maybe I will only miss one game."
One boost for Boro was the news that defender Andrew Taylor has been given the all-clear after suffering a toe problem.
"Andrew has been told he can carry on playing, he doesn't need to rest it and as far as we're aware he doesn't need an operation in the summer," said assistant manager Malcolm Crosby.
In other news young defenders Seb Hines and Rhys Williams have been ruled out for the rest of the season.