Linebacker Robert Caldwell and defensive tackle A.J. Ferguson were cleared to practice on Wednesday for N.C. State. The Wolfpack is still waiting on running back Mustafa Greene.
Caldwell, a junior college transfer, practiced for the first time on Wednesday. He had been held out while the school waited for clearance from the NCAA's Eligibility Center.
Ferguson and Greene had missed the first week of practice with academic issues.
"Ferguson's grades have posted, Mustafa's haven't yet," O'Brien said. "They've been able to work out because they're still eligible. That's where we are right now."
Greene missed the entire 2011 season with a foot injury. The team's leading rusher as a true freshman in 2010, Greene missed most of spring practice due to disciplinary issues with O'Brien.
Ferguson, a reserve defensive tackle, missed two games with a knee injury in 2011 and finished with a sack and seven tackles in seven games.
Greene, who ran for 597 yards and caught 30 passes, will have to pass running backs James Washington and Tony Creecy on the depth chart for playing time.
With three new starters at linebacker, and sophomore Michael Peek out for the season with a knee injury, the Pack needs to get Caldwell acclimated as soon as possible.
"That's one of the spots that we can ill afford to have an injury," O'Brien said.