O.J. Murdock, a Tennessee Titans reciever, committed suicide on Monday. He was only 25-years-old.

Murdock, who signed with the Titans in 2011 as an undrafted free agent, was found in his car outside his former high school, Middleton, in Tampa, Fla., at approximately 8:30 a.m., in critical condition. He suffered from a self-inflicted gunshot wound, police spokeswoman Andrea Davis said, according to The Associated Press.

Al McCray, who was an assistant coach for the football team while Murdock was at Middleton, received a text message from Murdock at 3:30 a.m., just hours before he committed suicide.

"Coach, I want to thank you for everything you've done for me and my family. It's greatly appreciated," the text said, according to McCray. "At the end, Murdock wrote: "I apologize."

Murdock was taken to Tampa General Hospital, where he died hours later.

Due to a right Achilles injury, Murdock never played one game while he was signed to the Titans, USA Today reported.

While it is not yet known why Murdock commited suicided, he is one of several NFL players in the past two years who have killed themselves.

Several years ago, a study linked sustaining three or more concussions to clinical depression, according to the NYTimes. Many NFL players report suffering from depression, mostly once they retire, and it is believed to be linked to head injuries during their career. This causes many to question how the NFL handles concussion-related injuries.

Take a look at several other players gone too soon.