EUGENE, Ore. (AP) -- Oregon quarterback Justin Roper will be out two to four weeks with a partial tear of a ligament in his left knee, coach Mike Bellotti said.

Roper injured his knee late in a 32-26 overtime victory at Purdue on Saturday.

Bellotti said the preliminary reports indicate a partial tear of Roper's medial collateral ligament in his knee. More tests were expected on Monday.

Roper was named starter for Oregon (3-0) in the week before the team's opener against Washington when projected starter Nate Costa injured his left knee in practice. Costa had surgery and is expected to miss the season.

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The No. 17 Ducks host Boise State on Saturday. The team is expected to use backup Jeremiah Masoli and true freshman Chris Harper at quarterback.

Both Masoli and Harper have played in all three of Oregon's games this season. Masoli, a junior college transfer, has completed 16 of 28 passes for 193 yards and two TDs. Harper has run for 102 yards and two touchdowns, while completing four of six passes for 40 yards and a TD.

Bellotti did not immediately name a starter for the game against the Broncos, but said both would likely play.

"Both have strong attributes and bring different strengths to the table," Bellotti said. "We can capitalize on their assets."

Oregon had planned on redshirting true freshman quarterback Darron Thomas, but he will be taking more snaps in practice, Bellotti said.