Suspended former Pittsburgh Steelers and Oakland Raiders wide receiver Martavis Bryant has formally applied to the NFL for reinstatement, a source told ESPN on Monday.

Bryant sent an email to league officials on Saturday, requesting reinstatement from an indefinite suspension the league imposed in December for Bryant's repeated violations of the league's drug policy.

Bryant, 27, was a fourth-round pick by the Steelers in 2014 but has missed 36 of a possible 80 regular-season games since then because of suspensions.

Last season, with the help of attorney Peter Ginsberg, Bryant was able to delay his suspension with an appeal by arguing that the league failed to properly address his mental health, including ADHD, a condition with which he was diagnosed as a child. Ultimately, the league rejected Bryant's appeal and imposed his third suspension in four years.

Since the end of last season, a source said, Bryant has worked with the NFL and the NFL Players Association to address his mental health and put himself in a position where he thinks his application for reinstatement has a chance to succeed. He has submitted to drug testing over the past couple of months and has consulted with the league and the union to find mental health professionals and get proper medication.

In May, the NFL and the NFLPA jointly announced the establishment of a new mental health and wellness committee, as well as a new regulation for 2019 that requires every team to employ a mental health professional who works in its building.

At the same time, the two entities established a joint pain management committee to conduct research into pain management and alternative therapies. That announcement has led many inside and outside the game to believe that change is coming in the league's policy on and attitude toward drugs such as marijuana.