Mark Convery will be sidelined for up to three months by the injury he suffered in Tuesday's defeat at Burton.
The midfielder limped off after a freak accident when Burton's John McGrath shoved Convery and sent him flying into Robbie Willmott, twisting the knee of his standing leg. Both U's men needed attention on the pitch while McGrath was booked, but although Willmott was able to continue, Convery had to limp off.
Consultant surgeon Mr Dennis Edwards made room in his schedule to see Mark the following day, and an MRI scan has confirmed that he has a ruptured medial collateral ligament.
"The knee was grossly unstable and Mr Edwards has confirmed my initial diagnosis," physio Greg Reid told cambridgeunited.com.
"Because of the mechanism of the injury we had to make sure there wasn't any damage to the anterior cruciate ligament as well, so he had an MRI scan done to make sure there was no other internal derangement within the knee.
"Thankfully it is just an isolated medial ligament injury but it's a very significant one so he's been put into a cast-brace, which is a cast above and below the knee with a hinged brace either side to allow a certain amount of movement."
Mark will keep the cast-brace on for the next six weeks, followed by an intensive rehabilitation programme, which is expected to last up to six weeks, so he could be sidelined until the middle of March.
Having enjoyed a run in the starting line-up in recent weeks, the injury comes at a frustrating time for the former Sunderland, Darlington and York midfielder, and the cause of the injury makes it even more frustrating, as Greg noted.

"The manner in which it happened is very disappointing too," he added. "He's been shoved and fallen into another player and it looks like such an innocuous thing, but unfortunately those sometimes cause the most damage."
We will keep you up to date with Mark's rehabilitation here on the official website.
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