LOS ANGELES — What has been expected for more than a week became official on Monday.

Quarterback Nico Iamaleava will miss the rest of the season for ninth-ranked UCLA after undergoing surgery for a knee injury sustained against Oregon, Coach Bob Chesney said Monday.

“It’s severe,” Chesney said, adding that the surgery would be later Monday or Tuesday.

Iamaleava got hurt late in the first half of a 17-15 victory over then-No. 13 Oregon on Oct. 10. He scrambled on a play and got tackled by two Oregon defenders, with his left leg getting twisted. After sitting out one series, he returned to the field, threw an interception just before halftime and didn’t return.

Iamaleava finished his second season in Westwood with 982 passing yards, four touchdowns and four interceptions to go with 144 yards rushing and one touchdown. He transferred from Tennessee last year.

Backup Ty Dieffenbach stepped in to finish the game and then made his first career FBS start in a 17-7 victory over Wisconsin last weekend. He went 22 of 33 for 264 yards.

The Bruins (6-0, 4-0 Big Ten) host Michigan State on Saturday at 12:30 p.m. at the Rose Bowl.

Injured UCLA quarterback Nico Iamaleava waves after the team's victory over Wisconsin on Saturday at the Rose Bowl. (AP Photo/Kyusung Gong)