Gordon, who turns 26 on April 16 and has served a drug suspension in all or part of each of the last four seasons, has been working out in Gainesville, Florida, with Montgomery.
Montgomery has had his own drug problems in the past. He served prison time after pleading guilty to possession and distribution of more than 100 grams of heroin in 2008 and was stripped of his medals and suspended in 2005 for using performance-enhancing drugs based on evidence gathered in the criminal investigation of the BALCO steroid scandal.
Since that time, Montgomery has rebuilt his life and is a coach and motivator at NUMA Speed, using his past mistakes to help others. According to NUMA Speed's website, Montgomery "focuses on helping athletes build self-confidence and avoid social and professional pitfalls in the face of substance abuse and peer pressure."
Gordon also changed agents this offseason and is now represented by Joby Branion, whose client list includes star Denver Broncos pass-rusher Von Miller -- a player who found himself in the NFL's drug program early in his career but managed to work his way out of it.
Gordon began the process of applying for reinstatement earlier this month, and sources said the expectation is that the NFL will make a decision by late April or early May. There's no guarantee of reinstatement, considering Gordon's history, but one source close to Gordon said he "embraces his role in his poor decision-making, which is half the battle."
He was conditionally reinstated last offseason and suspended for the first four games of 2016. But before that suspension ended, he entered a rehab facility and remained on the suspended list.
Gordon is still under contract with the Browns, but sources with knowledge of the team's plans have said they intend to move on from the troubled former star wideout and would either release him or try to trade him if he should be reinstated by the league.
In September of last season, when Gordon checked himself into rehab, Browns coach Hue Jackson said: "What's best for our football team is that we move forward and move on. He's not going to be with us, and we wish him well, but we're moving forward. We're going to move on.''