In their preseason loss to the 49ers, the Vikings’ troubles began by allowing 198 rushing yards in the first half.

Coach Leslie Frazier said that run defense would be an emphasis this week in Mankato. After Monday morning’s walk-through, DC Alan Williams reiterated that, saying the problems will be fixed in camp.

Williams said the defense's struggles were more mental than physical. The players weren’t in their proper gaps, he said, but they will be working on it this week.

“It may have been they [were in] their gaps, saw the ball go inside, went inside and the ball bounced outside,” said Williams. “There some problems with angles in terms of how guys got to the football. They ran hard, but we also said we want them to run smart. So when we get to that [point], it will be fine.”

The Vikings lost their best run stopper, NT Letroy Guion with a srained PCL early in the game. Guion is expected to miss one to two weeks. Williams said he liked what he saw out of Guion in the short time he played.

“The play that he went out on was a fantastic play,” said Williams. “We have preached great hustle throughout camp and on that play (Letroy) was downfield making a tackle."

Williams said Guion has shown he has a nonstop motor through OTAs and camp. He is stout up the middle and runs well enough to make tackles from sideline to sideline.

"I am pleased with how he is coming along,” Williams said.

When Guion returns, he will join DT Kevin Williams and DE Jared Allen, who were held out of the line up on Friday. That's another reason -- beside this week's emphasis -- Williams is confident the rush defense will improve. 

For more Vikings news and notes, follow Joe Oberle on Twitter @CBSSportsNFLMIN and @joeoberle.