HELENA, Mont. — Detroit Lions tight end Casey FitzSimmons has announced his retirement from the NFL due to injury.

Over his seven-year career, FitzSimmons has sustained several concussions, including one on Dec. 6 that caused him to end the 2009 season on the injured reserve list.

Following an evaluation by team doctors, FitzSimmons was advised by the Detroit Lions to retire.

In a statement released by his agent, FitzSimmons says deciding to retire was difficult but that he did so because of the seriousness of the risk associated with continuing to play.

FitzSimmons entered the NFL in 2003 as an undrafted free agent out of Carroll College, an NAIA school in Helena.