CORVALLIS - A major blow to the Oregon State football team's offense occurred when third-string running back Jeremy Francis left the team to be with his sick mother Marilyn Scott, coach Mike Riley said Tuesday.

Francis, a junior, went through finals last week and returned home to Winter Park, Fla., over the weekend. How long he'll be gone is unknown, but he's not expected to be available for the Sun Bowl.

"That's to be determined," Riley said of when Francis plans to return. "That's a personal decision by him. It's a wise decision by him. It's out of my hands. It's basically we'll wait and see."

Francis is a junior college transfer who has two more years to play one season. If he doesn't enroll next season he could use it as a redshirt year and still have one more season of eligibility.

Normally, losing the No. 3 running back isn't a big deal, but the Beavers are most likely without starter Jacquizz Rodgers as he recovers from an AC joint sprain.

That leaves redshirt freshman Ryan McCants as the only experienced running back on the roster. He started the season opener before Rodgers took over. McCants carried the ball 79 times for 314 yards and two touchdowns throughout the season.

"I'd say we are thin," Riley said. "We were in good shape a little while ago, but we are thin."

There are three other running backs on the roster with walk-on freshmen Jordan Jenkins, Clayton York and Josh Parish. Jenkins and York are redshirting, while Parish is a redshirt freshman.

York and Jenkins shared the work with the second string in practice. Riley, however, said there's no official backup at this point.

"We were working on a backup plan, but we do not have a backup running back," Riley said. "One (plan) is (finding) another back, and (the other is) what we are going to do in passing situations."

A partial fix on third downs may be using tight ends Joe Halahuni and Gabe Miller as blocking backs in the passing game, and on short-range passes.

Halahuni, however, hurt his previously injured knee at the end of practice. His status will be determined later.

Riley wouldn't say who would carry the ball if McCants was hurt if a decision was needed to be made today.

"We have to have a contingency plan for that," Riley said. "We are thinking about plans if something were to happen with Ryan in the ball game. We'll have that going soon. We have to have a couple options."

Francis and McCants shared the load filling in for Rodgers, who missed the Civil War and most of the Arizona game. Francis was the better third-down back as a receiver and pass blocker.

He had 20 carries for 89 yards and a touchdown and 12 receptions for 126 yards and a touchdown.

"We're doing stuff to work on different things and work in different people on the team," quarterback Lyle Moevao said. "We'll see how it goes."