ST. LOUIS-- Heisman Trophy winner Eric Crouch walked away from an NFL career, worn down by injuries and the challenge of learning a new position.

Crouch announced his retirement late Wednesday night after failing to make the transition from quarterback to wide receiver with the St. Louis Rams, who chose him in the third round of April's draft. His agent said he might return at some point and Rams coach Mike Martz said he'd be willing to listen if Crouch wanted to try again.

"The talent he had, he never gave it a chance," Martz said Thursday. "I really felt like his future here was going to be pretty dramatic, but it just didn't work out that way so you just send him on his way and wish him the best."

Crouch was back on the ground floor with the Rams after starring at Nebraska. He also pulled a hamstring and bruised a thigh, missing much of the preseason.

"His determination to learn everything and do the right thing, he just didn't know how to do it because it's all new to him," wide receivers coach Henry Ellard said. "As a star player, you're used to things going your way and knowing what you need to do, where here it was a different story."

Martz envisioned Crouch as a future star, a player with blazing speed that he could let run free from the slot, when he took him with the 95th overall pick of the draft. The Rams signed Crouch to a three-year, $1.3 million contract that included a $395,000 signing bonus.

Crouch has to give the bonus back after deciding last Friday that the NFL life was not for him. The Rams filled his spot on the 53-man roster Thursday by signing fullback J.R. Niklos from the Seattle Seahawks' practice squad.

"To each his own," defensive tackle Jeff Zgonina said. "It's only money, right?"

Crouch announced his retirement via fax and his agent, Jim Steiner, said his client would not do any interviews this week.

"The core of it is the injuries," Steiner said. "He's not able to get his body back to perform at a high level, the physical part of it affected him mentally, and he wanted to take a step back."

Steiner said Crouch isn't necessarily through with the NFL.

"He can always come back," Steiner said. "In the world of sports, retirement is not necessarily the end. The door is open for him to come back, and we'll just see how it develops."

Martz said there were no hard feelings.

"Absolutely, we would sit down and visit with him about the opportunity to come back," Martz said.

The news came as a bit of a shock to teammates who never got the chance to get to really know Crouch, let alone say good-bye.

"I thought he might take some time off and then really think about it," quarterback Kurt Warner said. "You're always surprised, with all the success he's had and the talent and everything, you never suspect something like this would happen or that he would choose to do that."

Ellard said it's tough enough for a young receiver coming out of college to make the transition to the NFL, let alone a quarterback trying a new position.

"Frustration comes in, and this offense can easily frustrate a guy because of all the little things we do," Ellard said.

Then came the injuries.

Crouch returned to practiced last week after being injured in the preseason opener Aug. 10 against Tennessee, and coach Martz said then he was "light years away from being ready."

That shouldn't have been a huge surprise for Crouch, even if he hadn't been injured. The Rams drafted him knowing it might take a while for him to make an impact and they've got one of the best receiving corps in the NFL without him.

"He was a project guy that you take under your wing and you bring them along slowly but surely," Ellard said. "We were in a situation where we could have done that with him.

"But all the success he's had, maybe that started to wear on him."