Nebraska coach Bo Pelini says Rex Burkhead's status for this week's game against Penn State is unclear.

The All-Big Ten running back has missed all or part of seven games because of an injury to his left knee.

Pelini said Monday Burkhead had been "pushing really hard" in his rehabilitation and had shown signs of improvement. The senior from Plano, Texas, didn't appear in the last two games after aggravating the injury in the first quarter against Northwestern on Oct. 20.

Burkhead, originally hurt in the opener against Southern Mississippi, is among seven running backs in Nebraska history to run for 3,000 career yards.

Ameer Abdullah has rushed for more than 100 yards in each of his four starts in Burkhead's place.