Oregon already had injury concerns about Heisman Trophy candidate LaMichael James. The status of quarterback Darron Thomas is also not certain now.
It's unclear whether both stars will play Saturday as the ninth-ranked Ducks try to extend their win streak to six and hand injury-plagued Colorado a fifth straight loss.
James dislocated his shoulder during a 43-15 win over California on Oct. 6 and sat out last Saturday's 41-27 victory over then-No. 18 Arizona State.
Oregon (5-1, 3-0 Pac-12) finished its latest win without Thomas, who injured his left knee and was replaced by Bryan Bennett with the Ducks leading 21-17.
Bennett finished 2 of 5 for 22 yards as Oregon mainly ran the ball with Kenjon Barner, James' usual backup.
"No one really knew what Brian can do and he came in the game when it was close, and it was difficult and he showed what he can do," James said. "And I'm really proud of him."
Thomas insisted he was fine after the game, but coach Chip Kelly has not committed to his starter just yet.
"I think the offense is the same so it's not like we run things different when Bryan is in there," Kelly said.
Barner, hampered by an ankle injury earlier in the season, ran for 171 yards with one touchdown last weekend. He and freshman De'Anthony Thomas have combined for eight rushing scores - the same total as James.
"I think I came out a little too amped up for myself," Barner said. "Instead of controlling my jitters, I let my jitters control me. Once the game got going I got into a groove."
James leads the nation with a rushing average of 170.4 yards. He said last Saturday that he felt he could have played, describing himself as at "80 percent."
Colorado (1-6, 0-3), meanwhile, has lost leading tackler Douglas Rippy to a season-ending knee injury and his cousin, top tailback Rodney Stewart, for up to a month.
The Buffaloes own the second-worst offense in the Pac-12 at 337.9 yards per game and the fourth-worst defense, allowing an average of 408.9 yards. Still, the Ducks are not taking them lightly.
"When you watch the tape, they play extremely hard," Kelly said. "They've lost a ton of players through attrition and they've got a ton of injuries right now but they play hard from the beginning of the game to the end of the game."
Colorado has conceded 100 points over its last two games, falling 52-24 at Washington last Saturday. The Buffaloes know improvement won't be easy against an Oregon team scoring 48.7 points per game for the nation's third-highest average.
"Oregon, it's not just their offense but their whole team," coach Jon Embree said. "The thing that jumps out about them is just their speed. They have great speed at all their skill positions. They do a tremendous job of making you defend the entire field."
The Ducks will take aim at Colorado's Tyler Hansen, who has been sacked a Pac-12-high 19 times. Hansen has done a good job of protecting the ball with 13 touchdowns to three interceptions.
Tony Jones will replace Stewart as the starting tailback. He's carried 31 times for 116 yards, and Embree insists he will continue to try to run the ball.
The Buffaloes also remain without top receiver Paul Richardson due to a knee injury, while receiver Kyle Cefalo is out with a knee sprain suffered last week.
Colorado is playing at home for the first time since Oct. 1, and Oregon isn't doing anything specific to prepare for the altitude.
"Well we haven't played there yet," Kelly said. "There's nothing we can do about it so we don't really talk about it. We can't move the Moshofsky Center (training facility) higher to get ready for practice."
Colorado leads the all-time series 8-7. The Ducks won the last meeting 38-16 in the 2002 Fiesta Bowl.