He was strechered off injured in the first half of Boro's defeat at Arsenal after a challenge by Gio van Bronckhorst. He is believed to have aggravated a knee injury he has been carrying for some time, and which nearly forced him to miss the game in the first place.
Boss McClaren was understandably worried, " Hes been feeling a niggling knee injury for a couple of weeks. We'll know the full extent in the next 24 hours but it didn't look too good."
Boateng is definitely out for the Boxing Day clash against Manchester United, but he could be out for a lot longer if the damage is serious.
One plus point Boro was the amazing return to action by Joseph Job. He fractured a skull 3 weeks ago at West Brom and has amazed everyone with his return to action.