Zimmer told Vikings players in a team meeting Monday morning that Cassel would be the starter over rookie Teddy Bridgewater, who had played well in the preseason and directed a game-winning touchdown drive Aug. 16 against the Cardinals.
But Cassel has received the majority of the first-team work, playing nearly three full quarters in the Vikings' third preseason game in Kansas City on Saturday night. His installation as the starting quarterback seemed inevitable for several weeks; Zimmer made it official Monday.
"At this stage and where we're at right now, that's the best thing to do," Zimmer said. "I told Teddy this morning that I'm so happy he's here with us. We like everything that he's done. It wasn't anything that Teddy did or didn't do. Teddy will be, still, in my estimation, a great player for this franchise for years to come."
Cassel, who has completed 26 of 39 passes for 367 yards, two touchdowns and an interception in the preseason, started six games for the Vikings last season, including their final four, and signed a new two-year, $10 million deal after opting out of his original 2014 contract in February.
Now he's in line to get an opening-day start for the first time in two years.
"I worked tremendously hard this offseason to put myself in this position," Cassel said. "I'm excited that it's gone the way that it has. I've played well in preseason, and Coach [Zimmer] has given me the confidence and the trust to go along and name me the starter."
Zimmer said the Vikings won't treat the quarterback position any different than any other spot on the roster, adding "If you perform, you'll play." Cassel, though, seems to have the confidence of veteran players and will give the Vikings a chance to groom Bridgewater, instead of putting him on the field during a potentially difficult early-season schedule that includes dates with the Patriots, Saints and Packers in a 3½-week span.
"Once I got drafted, I felt this was the perfect situation for me," Bridgewater said. "Right now, I'm able to just learn but also prepare myself as a starter. It's a great situation for me."