"We just felt like it was, from a medical standpoint, too risky to put him out there to take a hit," Frazier said.
On Thursday, Ponder said he made progress from his injury but acknowledged that his status would be determined after consulting with Frazier and the team's head athletic trainer.
When asked if this was his opportunity to win the job permanently, Cassel said he is just focused on winning this Sunday and "being accountable" to his teammates.
LOOKING FOR A WIN AT WEMBLEY
The Vikings and Steelers are both 0-3 heading into Sunday's game at Wembley Stadium.
"We're both trying to get this thing started and turn the season around," Cassel said. "So obviously it's very important game for both teams and were going to do whatever we can to come out of here with a W."
The decision to start Cassel was semi-leaked by New England Patriots quarterback Tom Brady during his Wednesday press conference, when he was asked about his former backup and current Browns starter, Brian Hoyer.
"We have a great relationship and a very close relationship," Brady said. "The backup quarterback, there's only been two of us, Brian and I at one time and now myself and Ryan Mallett. We have a great rapport. I'm friends with all those guys. Matt Cassel, I talk to. He may be starting this weekend."