Lions tight end Casey FitzSimmons announced his retirement Wednesday from the NFL due to several concussions. A concussion he suffered in December is still giving him problems. "This has been a very difficult decision," FitzSimmons said in a statement released by his agent. "I feel like 2009 was one of the best seasons of my career, because I was so consistent, and was able to contribute in a variety of ways. If it wasn't for the concussions, I would not be retiring. "It's frustrating because the rest of my body is still capable of playing at a high level in the NFL," he said. "However, given the seriousness of the risk associated with continuing to play, I have to listen to the advice the team has given me."