Ponder had taken the majority of snaps in practice Thursday and looked determined to play Sunday.
"We just felt like it was, from a medical standpoint, too risky to put him out there to take a hit," Frazier said. "He's a tough guy but it probably wouldn't be wise to put him out in that situation."
"He's a competitive guy and he's played through some tough injuries here. He wanted to play," Frazier said. "This is something you don't know how many times you'll get a chance to play in a game like this, but it's probably wise since we have a bye coming up, so he understands."
Also ruled out for the Vikings are cornerback Chris Cook (groin), safety Jamarca Sanford (hamstring), and tight end Rhett Ellison (knee).
The rest of the players on the Vikings' injury report all practiced in full Friday and are probable for Sunday's game. They are running back Matt Asiata (hamstring), cornerback A.J. Jefferson (ankle), defensive tackle Kevin Williams (knee), linebacker Erin Henderson (heel), and long snapper Cullen Loeffler (neck).
The Vikings and Steelers are both 0-3 heading into the NFL International Series match at Wembley Stadium.
Online: AP NFL website: http://www.pro32.ap.org