LONDON -- Vikings coach Leslie Frazier said the team hopes Christian Ponder is able to do more work in practice Thursday after being limited on Wednesday because of his rib injury.

Frazier said Ponder experienced "some soreness" on Wednesday, which prevented him from doing as much work as the team had hoped. Matt Cassel took the majority of snaps.

"We're going to try and give Christian more today to see if he can handle it and try and make a decision by Friday," Frazier said.

Frazier said the team likely will make a decision on Ponder after Friday's practice as opposed to a game-time decision.

"Probably if he couldn't do anything on Friday to where we felt comfortable, we probably wouldn't put him out there if we didn't see what we needed to see on Friday," Frazier said.

Ponder's injury raised speculation that the Vikings saw this as a convenient opportunity to make a quarterback switch. Frazier dismissed that conspiracy theory.

"It's purely circumstantial if that happens," Frazier said. "We want Christian to play. We want him to get out there and continue to grow and develop as a quarterback. But we signed Matt Cassel for occasions just like this, if something were to happen to Christian. We'll see what happens."

Secondary health update

Frazier didn't sound optimistic that cornerback Chris Cook will be able to play Sunday. Cook was not expected to practice Thursday because of a groin injury.

"If he's not able to [practice] today or tomorrow, it's highly unlikely he'll be able to play in the game," Frazier said. "I think the fact that he's not able to practice today leads you to believe that it may difficult tomorrow. But he wants to try tomorrow so we'll see."

Frazier said A.J. Jefferson (ankle) will practice Thursday and possibly safety Jamarca Sanford (hamstring). Frazier said Cook's situation might force the team to make a roster move, possibly promote Robert Steeples from the practice squad.

"If A.J. is not able to go today, we may have to do something like that because you don't want to go into this game with only three healthy corners, especially with all the three wide receivers sets that they show," Frazier said. "We'd have to look at doing something. It just would not be wise playing with three corners."