Michael Sam, the first openly-gay player picked in the NFL draft, is stepping away from professional football.
Sam, who made history when he was selected in the seventh round by the St Louis Rams in 2014, has told the Canadian Football League's Montreal Alouettes that he is leaving the team.
The 25-year-old defensive end announced his decision on Twitter on Friday, citing concerns about his mental state as his reason for doing so.
He wrote: "The last 12 months have been very difficult for me, to the point where I became concerned with my mental health.
"Because of this I am going to step away from the game at this time."
Sam thanked the Alouettes, with whom he signed a two-year contract in May, and added he hoped to return soon.
The Alouettes confirmed in a release that Sam has left the club for "personal reasons" and that he has been added to the team's suspended list.
He did not play in Montreal's home loss to Edmonton on Thursday night, with the team citing a sore back. He made his CFL debut the previous week.
Sam, the 2013 Southeastern Conference defensive player of the year at Missouri, failed to record a tackle in Montreal's loss to Ottawa.
He agreed to a two-year deal with the Alouettes this summer. He left training camp on June 12, citing personal reasons, and sat out the team's first five games.
Sam failed to make the Rams 53-man roster last season out of training camp and spent time on the Dallas Cowboys practice squad before being released.