Roughriders quarterback Zach Collaros didn’t return to practice after the team's bye week.

The Riders had their first practice since losing to the Calgary Stampeders 37-10 on July 6.

Collaros hasn’t played since the early minutes of the Riders' season opener in Hamilton in June. A late hit by Tiger-Cats' Simoni Lawrence knocked him out of the game with a head injury. He was placed on the six-game injured list shortly after the hit.

An arbitrator upheld the CFL's original two-game suspension of Lawrence on Tuesday. He will miss a rematch against the Riders at Mosaic Stadium on Aug. 1.

Collaros has missed the last three games.

Head Coach Craig Dickenson said Collaros can't practice because he is still on the six-game injured list. The quarterback is taking part in meetings and workouts, and the team is monitoring him.

Injured kicker Brett Lauther was at Tuesday's practice at Mosaic Stadium, but wasn’t participating in any drills. Defensive back Nick Marshall was taking reps after sitting in the Riders' last game.

The Riders take on the B.C. Lions on Saturday evening.

With files from CTV Regina's Claire Hanna