Defender to miss three months.
Boss Joe Dunne explained: "Josh needs an ankle operation, and that will keep him out for three months.
The former Celtic and Portsmouth man had been making steady progress in his rehabilitation, but now will go under the surgeon's knife.
U's central defender Josh Thompson is set for an extended spell on the sidelines after being told he needs an operation on his ankle.
"He had been making some progress in rehab, and had reached a certain point in his recovery, but the ankle is still very sore.
"Josh visited the specialist on Wednesday for further investigation of his ankle, and it has now been agreed that he should have the operation."