Brandon Meriweather after being hurt during the preseason (Charles Rex Arbogast/The Associated Press)

Safety Brandon Meriweather will undergo an MRI exam on his left knee after re-injuring it during pregame warmups before the Washington Redskins’ triumph Sunday over the Tampa Bay Buccaneers, Coach Mike Shanahan said.

Meriweather and wide receiver Aldrick Robinson were on the Redskins’ inactive list after colliding on the field while warming up for the game. Robinson suffered a concussion and was unconscious “for about a minute or so,” according to Shanahan.

“I’ve never had that in my coaching career, to have two guys go out in pregame,” Shanahan said. “Luckily it was more than the hour and a half before you put in the 46 [active] players.”

   Shanahan said Meriweather’s knee was “quite sore” but he didn’t know the extent of the latest damage to the safety’s knee.

Meriweather was ready to play Sunday before the pregame incident, Shanahan said.

Meriweather hasn’t played all season. He initially injured his knee in the second preseason game, then aggravated the injury in practice six days before the Redskins’ season-opening triumph at New Orleans.