Stills suffered the concussion against Florida State and complained of headaches late last week, prompting team doctors to hold him out.
"I learned a lesson. I should keep my mouth shut. If I want to be in the game I shouldn't be saying anything. I want to be on the field at all costs," Stills said, half-jokingly.
Stills dressed, got taped up and warmed up with the team.
"I begged until kickoff to play," he said.
But doctors wouldn't budge. Stills has resumed practice this week and should be good to go this weekend.
"I definitely feel like I've missed out," he said. "But it motivates me even more to play."
Stills missed the Sooners' opener against Tulsa due to suspension. He caught seven passes for 125 yards, including the game-winning touchdown, in OU's win over Florida State.