Montgomery has helped mentor Gordon, according to Mary Kay Cabot of Cleveland.com, and he said Gordon will be out of rehab on Sept. 21 after a 90-day stint.
Montgomery expressed confidence that the NFL will end Gordon's suspension once he is able to apply for reinstatement: "He's been clean, so we're hoping after 90 days he's reinstated and they put him back in the league, which it looks like they're going to do that."
According to Spotrac, the NFL has suspended Gordon on three different occasions for violating its substance abuse policy.
He missed all but five games in 2014, as well as the entire 2015 and 2016 campaigns.
The NFL conditionally reinstated Gordon last July, and he was slated to return to the Browns in Week 5 of the 2016 season. However, the league placed him back on indefinite suspension when he left the team to check into inpatient rehab.
Montgomery said the NFL told Gordon he could apply again in the fall, and the former gold medalist believes Gordon is finally in a good place: "From what I've seen, he's in a different place than what he was six, seven months ago. He's come a long, long way from when we first started working together."
It isn't yet known if the Browns will welcome Gordon back or if they'll release or trade him in the event the league does reinstate him, but Montgomery doesn't expect it to take long for him to be in football shape.
The 2013 season was the last time Gordon played extensively, and it remains his career-best year.
He was named a Pro Bowler and a first-team All-Pro, as he made 87 receptions for a league-leading 1,646 yards and nine touchdowns in 14 contests.
Cleveland lacks quality receivers for rookie quarterback DeShone Kizer behind current starters Corey Coleman and Kenny Britt. If the NFL does reinstate Gordon and he returns to the Browns, it could provide a significant boost to the team's offense.