Stuart Holden is set to be out of action for between six and nine months after an operation on ligaments in his right knee.
The American international was forced off in last week’s specially arranged under-21 game against Everton at the Reebok Stadium.
And after heading back to the US for scans and further assessments from the specialists who completed his operation in the summer, Holden has now had a further operation.
Dougie Freedman said: “Unfortunately, Stuart’s knee has gone. His surgeon has had a look and has deemed this to be the best course of action.
“We’re all obviously very disappointed for Stuart, but he’s a warrior and a fighter and someone who knows exactly what he wants to achieve.
“Everyone at the football club is right behind him.”