The 31-year-old told reporters: "I'm not really looking ahead, to be completely honest. I just found out [yesterday] morning.
"For me, it's really about going out there, being accountable to my teammates and hopefully, getting out of here with a win this weekend."
Head coach Leslie Frazier added: "I don't foresee a quarterback controversy. But we want [Cassel] to play lights-out, want him to have the best game of his NFL career on Sunday."
The Vikings face the Pittsburgh Steelers tomorrow evening.