The Vikings open the season Sept. 7 on the road against the St. Louis Rams.
Cassel has started each of Minnesota's three preseason games, completing 26-of-39 passes for 367 yards, two touchdowns and one interception.
Bridgewater was the team’s first-round pick in the May’s draft. In the team’s last preseason game against the Kansas City Chiefs, Bridgewater completed 4 of his 7 passing attempts for 40 yards and two touchdowns.
"I told Teddy this morning that it was not anything he did or didn't do," Vikings head coach Mike Zimmer said. "We will hold the quarterback position to the expectation that we hold all positions. If you perform, you'll play."
Cassel, 32, started six games last season for the Vikings, going 3-3 in those contests. He completed 60.2 percent of his passes for 1,807 yards, 11 touchdowns and nine interceptions.
- Scooby Axson