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Michael Sam, newly signed defensive end for the Montreal Alouettes CFL football team, talks to the media following his first day of rookie training camp in Sherbrooke, Quebec May 27, 2015. Reuters

In a series of tweets on Friday, Michael Sam announced that he was stepping away from football following a year of setbacks in his professional career. Citing a difficult last year in which he felt concern for his mental health at times, Sam thanked the Montreal Alouettes for giving him the opportunity to play on the team and said he hoped to be back playing soon.

About a year ago, Sam was cut from the St. Louis Rams in a final round of cuts before the season started. A rookie, Sam then moved on to play for the Dallas Cowboys' practice team, where he was cut again. He became nationally famous when he was drafted in 2014 as the first openly gay football player.

From his Twitter account, which has a profile picture of him wearing his college jersey, Sam explained his decision to followers.

His step away from football follows his professional football debut last week, when he played a lukewarm game for the Alouettes in which he was unable to make a tackle during 12 plays while he was on the field and was badly fooled during a play that allowed the opposing team, Ottawa, to get a touchdown. His time with the Alouettes was contentious, and it was said that he walked out on teammates and took two weeks away from the team's training camp for personal reasons.

Sam made national headlines when he told his teammates during an ESPN interview in 2014 that he was gay. He had previously come out to his teammates at the University of Missouri, where he played in college, and found that they were supportive. His coming out stirred some controversy, including protests from the Westboro Baptist Church.

While a player for the University of Missouri, Sam was a celebrated defensive player. He earned several awards and accolades and frequently started on the varsity team his senior year.