He tore an anterior cruciate ligament while conceding what turned out to be the winning goal on April 4.
It was a recurrence of an injury he first picked up against Chesterfield on March 4.
Glovers. boss Steve Thompson said: "I am gutted with the news.
"The club have spared no expense, the surgeon looking after Chris operated on the Queen's knee and you can't get a better recommendation than that.
"It will be a long tough job and he will have to both dedicated and patient."