The move wasn't a surprise. Dressler, 28, was scheduled to become a free agent Feb. 15 and was exploring his NFL options.
This allows Dressler, who earlier this month worked out for the Kansas City Chiefs, to sign an NFL deal immediately.
Riders assistant GM Jeremy O'Day said that could happen very soon.
"Weston and his agent were very up front they were going to go through the process and we were made aware of a possible situation coming up in the next couple of days where Weston was more than likely going to get an opportunity," O'Day told reporters. "From our standpoint it's tough to lose such a good player that's been here for a long time, is a leader in the locker-room.
"But again, you've got to feel happy for him that he gets that opportunity. He hasn't gone through the process of being in the NFL and as any competitor you just want to see how you compare with the best available players. We wish him the best."
The five-foot-eight, 179-pound native of Bismarck, N.D., has spent the past six seasons in Regina, having registered 442 catches for 6,531 yards and 43 TDs. He has surpassed the 1,000-yard receiving plateau five times in his career, including the last four years.
Dressler had five catches for a game-high 81 yards and a touchdown in Saskatchewan's 45-23 Grey Cup victory over Hamilton.
Dressler is a two-time CFL all-star and was the league's top rookie in '08.
"For the team obviously it's not great news," O'Day said. "But it's our job to find good players and hopefully we'll be able to replace him."