The former Nebraska pass-rusher and current Dallas Cowboy was suspended indefinitely on Tuesday, the team announced.
Gregory was suspended for violating the league's substance abuse policy and the terms of his previous conditional reinstatement to the league, the Cowboys said.
The prolific edge rusher was coming off a productive season, too, having played in a career-best 14 games and compiling six sacks.
Gregory was a two-year star at Nebraska before being taken in the second round of the 2015 NFL Draft by the Cowboys.
Gregory, though, has played in just 28 career games (12 in 2015, two in 2016 and then a nearly full season last year) around the multiple suspensions.