TUCSON, Ariz. (AP) -Oregon quarterback Dennis Dixon left the Ducks' game at Arizona because of a knee injury in the first quarter.

Dixon's left knee appeared to buckle as he tried to plant on an option carry with about 5 minutes to go in the quarter.

Dixon, a leading Heisman Trophy candidate, sprained the same knee against Arizona State on Nov. 3. He wore a brace Thursday night.

Dixon had a 39-yard touchdown run on the Ducks' first possession. He was 5-of-8 for 62 yards and threw an interception in the end zone.

Senior Brady Leaf replaced Dixon.