Ravens backup running back Bernard Pierce suffered a hit to the head on a high tackle by Washington Redskins safety Brandon Meriweather, sustaining a concussion in the first quarter.
Pierce went to the locker room with team doctors to be further examined under the mandatory NFL concussion testing protocol and remained under observation in the second half and didn't return.
Pierce got shaken up after being tackled for a five-yard loss. He started the game and rushed for minus-three yards on four carries.
"We'll have to see," said Ravens coach John Harbaugh, adding that there were no other serious injuries. "I'm not sure where he's at right now. He obviously didn't return in the game. His head, we'll just have to see how that goes."
Pierce is slated to start during three-time Pro Bowl running back Ray Rice during Rice's pending two-game suspension for violating the NFL personal-conduct policy, a punishment stemming from a felony aggravated assault charge from a domestic violence case.
Rice didn't play at all and Harbaugh declined to elaborate on whether he'll play in the fourth and final preseason game next week against the New Orleans Saints.
"That was our plan this week," Harbaugh said. "So, next week we'll let you know. You'll see it when you see it."
Meriweather has a long history of illegal hits, but the tackle on Pierce was legal because he was the primary ball carrier. Meriweather wasn't flagged on the play.
"It was just executed well," Meriweather said. "They did not see me coming. When I came in, I squared him up, and they called the play right into the blitz."
Meriweather was fined $50,000 during the 2010 for a helmet-to-helmet hit on former Ravens tight end Todd Heap.
Last season, Meriweather was suspended two games for repeated violations of the NFL's rules against helmet-to-helmet hits for a pair of illegal shots on Chicago Bears wide receivers Brandon Marshall and Alshon Jeffery. He was suspended for two games without pay, but it was later amended to a one-game suspension that cost Meriweather $70,588.
Earlier last season, Meriweather was fined $42,000 earlier in the year for an illegal hit on Green Bay Packers rookie running back Eddie Lacy.
Meriweather is aware of the scrutiny he's under from the NFL.
"I think they've been keeping a close eye on me for the last couple years," he said. "I'm just going to continue to work on my game and try to get lower to do the things they want me to do."