Bolton have confirmed goalkeeper Andy Lonergan will spend five to six weeks recovering from surgery.
The stopper suffered damage to his cartilage during a training ground accident last week.
Caretaker boss Jimmy Phillips said: "Andy Lonergan unfortunately before the Bristol City game, in a very innocuous training incident, had a cartilage problem.
"He had that operated on in London so he's going to be out for, I think, five or six weeks."
Lonergan has failed to displace Adam Bogdan as Wanderers' first-choice stopper since signing from Leeds over the summer.