Leary has been in the concussion protocol since Monday night's regular-season opener against the Los Angeles Chargers. Leary did not play in the second half of the Broncos' 24-21 win and has not taken part in a full practice.
He was formally listed as questionable for Sunday's game but would have to be cleared in multiple steps in the league's protocol, by an independent physician, before he can play against the Cowboys.
"He was out there (Friday), that part he's passed," head coach Vance Joseph said. "There are a couple more things he has to pass before he can play."
Safety Darian Stewart (groin) was also listed as questionable for the game, but Joseph has expressed optimism through the week that Stewart would be able to play against the Cowboys.
"Darian looks good," Joseph said after Friday's practice "And I'm hoping he continues to progress and obviously play in the football game."
With defensive end Jared Crick (back surgery) now on injured reserve, the Broncos were trying to get Ahtyba Rubin up to speed in the defense. Rubin, who started 16 games in each of the past two seasons in Seattle, was among the last of the Seahawks cuts after the team had acquired Sheldon Richardson in a trade.
"He flew in (Thursday) night had his physical (Friday) morning," Joseph said. "(It's) very possible (he'll play)."
Joseph said it should be a fairly easy transition into the Broncos defense. With defensive end Zach Kerr (knee) also questionable for the game, the Broncos could use Rubin to be ready to play against the Cowboys' run-first offense.
"He's been a 16-game starter for two years in Seattle and they're known for having a hell of a defensive front," Joseph said. "You watch the guy's tape, he's a big man, plays really hard. As far as the run game he's very stout, he's got some inside pass rush also. I'm happy to have the guy, a guy who's played so much at a high level."