"Jamal Lewis suffered a serious concussion Sunday in Cincinnati and visited a brain trauma specialist on Wednesday, said a source with knowledge of the situation.

Lewis, who previously announced this would be his last NFL season, has played his last down of football. He will retire as the 21st leading NFL rusher with 10,607 yards in 131 career games.

But Lewis' place on the all-time rushing list is the furthest thing from his mind.

A source said that Lewis was "pretty shaken up" when an MRI test showed "brain abnormalities." They may be the result of excessive trauma triggered by a recent hit. More tests will be done to determine the extent of Lewis' injury, the source said.

Lewis' last carry in Cincinnati was for one yard with 14:02 left in the fourth quarter. He was on the field for the next play for the last time. The Browns threw the ball on their last 19 consecutive plays, as they trailed, 16-7.

The club did not announce that Lewis suffered an injury during Sunday's game. Coach Eric Mangini made no mention of Lewis' injury on Monday or Wednesday.

The club's regular Wednesday injury report listed Lewis as "out" with a head injury. It wasn't until early evening that the Browns acknowledged the seriousness of Lewis' injury when they announced he was put on injured reserve because of post concussion symptoms.

The Browns did not confirm Lewis was being examined by a specialist.

Safety Brodney Pool also was put on the season-ending list after suffering the fourth concussion of his career in Sunday's game.

"After consulting with our medical team, we felt that this was in the best interests of both Jamal and Brodney at this time," Mangini said in a statement. "As I've said before, organizationally, players' health and safety are paramount in any decision we make with regards to putting them back on the field.

"Jamal has been an integral part of this team and he has exhibited a great work ethic. He worked hard, studied hard and set a good example for the younger running backs.

"I'm disappointed that Jamal and Brodney are not going to be able to finish out the season, and I thank them both for their contributions this year."

Pool could be pondering retirement at the age of 25. His contract with the Browns is up after this season.

Teammate Abram Elam said that he spoke with Pool Wednesday morning and reported, "He's in good spirits, just following doctor's orders."

The injuries to Lewis and Pool really bring home the wave of concussion awareness currently sweeping the NFL. Recent concussion injuries suffered by Philadelphia running back Brian Westbrook, Washington running back Clinton Portis, Arizona quarterback Kurt Warner and Pittsburgh quarterback Ben Roethlisberger accentuated national attention on the NFL's need to deal better with head injuries.

Last month, the House Judiciary Committee held hearings on the subject, which resulted in new guid