Vikings cornerback Captain Munnerlyn will undergo a MRI on Monday after he was knocked out of Sunday's loss to the Lions during the first half.
Munnerlyn, who was already nursing a foot injury, suffered knee and ankle injuries that had him with a brace on his right knee after the game. He was being fitted for crutches while answering questions about his injuries after the game.
"I consider myself a tough guy," Munnerlyn said. "But couldn't do it."
Munnerlyn made a brief exit for the locker room and underwent X-rays before returning for one snap. After tackling Lions receiver Anquan Boldin on a catch, Munnerlyn said he knew he couldn't continue playing.
"I dove at him and couldn't get up," Munnerlyn said.
The Vikings turned to rookie Mackensie Alexander, who was flagged for defensive holding at the goal line and then allowed a one-yard touchdown catch that gave the Lions a 10-3 lead.
Vikings head coach Mike Zimmer then moved veteran cornerback Terence Newman into the slot, where he played the rest of the game with Xavier Rhodes and Trae Waynes on the outsides.
The Vikings also lost punt returner Marcus Sherels early in the game to an ankle injury. Sherels missed last week's loss in Chicago because of an injured wrist.
