Cassel will start over Christian Ponder, who suffered a rib injury in Week 3.
Ponder, the third-year starter in Minnesota, revealed he hurt his ribs during the Vikings' loss to Cleveland last Sunday.
Ponder did not participate Friday, in London, where his Vikings will play the NFL's seventh game in England.
Going into the game, the Vikings and their opponents, the Steelers, are both 0-3.
Quick Stats:
- Cassel signed a two-year contract this off-season.
- Cassel started 62 games during his nine-year career (New England, Kansas City, Minnesota).
- Cassel went to the Pro Bowl in 2010 - after throwing 27 touchdowns.
