COLUMBUS, Ohio - Ohio State freshman tailback Maurice Clarett re-injured his left shoulder early in the first quarter of the Buckeyes' 13-7 win over Penn State on Saturday and did not return.

Clarett, who entered the game with 980 yards rushing, carried four times for 39 yards to top the 1,000-yard mark for the season. But on a 9-yard gain, his shoulder turned underneath him as he was tackled.

It is unknown how long Clarett will be out. Clarett was hampered by a stinger in his left shoulder a week ago at Wisconsin.

"His shoulder has been sore for a number of weeks," Ohio State coach Jim Tressel said. "It's the pounding you take when you play at this level. He hit it just right and was not capable of coming back."

Clarett came to the sideline and tossed aside his helmet as he was attended by Ohio State team doctors. He later took off his shoulder pads and watched the rest of the game from the bench.

Tressel said he did not know the severity of Clarett's injury. The Buckeyes play Minnesota on Saturday.

"I can't tell you if it's a one-day thing or a five-day thing," Tressel said.