Jake Leake has undergone surgery on his shoulder.
The U's summer signing fell awkwardly in the opening game of the League Two season and dislocated his shoulder.
Early indications were that it would heal without having to go under the knife, but further examinations have concluded that an operation was needed.
That operation took place on Thursday, with Head Coach Danny Cowley hoping that Jake will recover as soon as possible.
He said: "It's disappointing news, for us and of course for Jake."
"It was that bad fall at Accrington, but we never thought it was so serious then.
"It looked like we might be able to get him back without the surgery, but it wasn't the case.