The 6-foot, 201-pound Campbell appeared in two games this season and started one. He missed one game due to a suspension for violation of team rules and missed the last three because of recurring headaches.
Sumlin said that Campbell's headaches began before the Aggies' Sept. 29 game against Arkansas and he was evaluated for a concussion. Campbell did not play against the Razorbacks and hasn't played since.
According to Texas A&M associate athletic director Alan Cannon, Campbell has sustained concussions previously while at A&M. Injuries to his shoulder, foot and knee also have interrupted Campbell's career in the last two seasons.
The coaching staff has proceeded with caution with Campbell since he missed the Arkansas game. Sumlin said he spoke with Campbell, who indicated that he was done playing.
"After talking with the doctors and his feelings, Steven's not going to play any more," Sumlin said. "After the concussions and just his general feeling, I think his exact words were, 'I just don't feel like myself right now.' It's just not worth risking, so he's going to go to school and graduate."
Sumlin said the coaching staff will always take concussions seriously.
"We're going to err on the side of safety," he said. "That was a deal where we took our time with Steven and sat down with the doctors and that's nothing that you joke about. We take that very seriously."
Sophomore Deshazor Everett is listed as the starter in Campbell's place heading into the Aggies' game against LSU this week.