Green apologized in a statement. He says he was trying to gain weight during the offseason and took a supplement given to him by someone from his hometown in Macon, Ga.
He says he "wasn't responsible enough to check with our coaches to make sure that it was something legal and now I'm paying the consequences."
The 6-foot-4, 220-pound Green had 28 tackles, one sack and one interception in seven games last season with the Wolfpack. He missed the final five games with an unspecified foot injury.
Green, a sophomore, will be allowed to practice with the team but cannot play in games.