Magnus ruptures Achilles tendon.
The U's skipper has ruptured his Achilles tendon and could now miss the rest of the season.
"Around five or six months is the projected recovery time, so it looks like it could be the rest of the season for him."
"He has had a stop start season with suspensions and a hamstring injury and now has this injury to contend with.
U's boss Tony Humes said: "It's a massive blow for Magnus and I really feel for him at the moment.
Initial fears were that it was serious and they were confirmed on Monday and the operation to replace the tendon will go ahead on Thursday.
He was helped to the sidelines but needed a stretcher to get to the changing rooms at the Weston Homes Community Stadium.
An aerial challenge in the closing minutes of Saturday's game against Coventry City looked innocuous but it left Okuonghae on the deck.