With Marc Tierney out of action after dislocating his shoulder against Dagenham & Redbridge, John Ward has moved quickly to bring in cover, signing Tom Williams on loan from Bristol City.
The 30-year-old full back has signed on a month's emergency loan and is expected to go straight into the squad to face MK Dons on Saturday.
Meanwhile, Ben Coker, who has yet to make a first team appearance for the U's since signing from Bury Town, has joined Chelmsford City on loan for a month.