Vikings coach Leslie Frazier hadn't seen the chop block that took out Kevin Williams' right knee when asked about it after Sunday night's 34-14 preseason loss at San Francisco.

Frazier's assistant coaches looking on from the press box certainly had seen it. And they were ticked that 49ers second-year backup guard Joe Looney chose to chop Williams at the knees. On a third-quarter play in which several defenders were scrambling about before a tackle for loss, Williams was moving to his right, away from the play, when Looney peeled back toward Williams, who never saw the block coming. Looney ducked his head and shoulders, buckling the knee. Williams was able to walk off the field on his own, but he's had or will have an MRI performed today. The Vikings are concerned the injury could be serious.

Update: The Vikings issued this statement: "Kevin Williams suffered a hyperextension injury to his right knee in last night's football game. An MRI exam today revealed a significant bone contusion as well as a posterior capsular strain. Kevin was fortunate in that there was no injury to any of his ligaments." – Head Coach Leslie Frazier

"The guys upstairs were telling me that was one of those plays where we will probably want to send it into the league," Frazier said. "They were pretty upset when they saw it."

There was no flag on the play, but Williams wasn't happy that a second-year guy chose to unnecessarily chop block an 11-year veteran in a preseason game.

The Vikings also want the league to weigh in to see if the block violated the new rule against peel-back blocks.The NFL banned all peel-back blocks below the waist, from the side and from behind, even inside the tackle box, at the spring owners meetings this year. Peel-back blocks of this nature outside the tackle box have been banned since 2005.

Looney did hit Williams from the front, so it remains to be seen how the league will interpret the legality of the hit based on the wording of the rule. Either way, the Vikings considered Looney's actions to be a low blow, both literally and figuratively.