In the aftermath of a questionable low block on Pro Bowl defensive tackle Kevin Williams Minnesota Viking defenders called for the NFL to provide some modicum of justice.

But San Francisco 49ers backup guard Joe Looney wasn't penalized in the third quarter of Sunday's preseason game and he wasn't penalized by the NFL on Tuesday.

"It was a legal play" said Greg Aiello the NFL's senior vice president of communications. "It's not the new rule on the peel-back block because Looney was not moving toward his own goal line."

That explanation didn't sit well with several Vikings after Tuesday's practice.

"We talk about player safety. You talk about wanting to protect us. How is he not a defenseless player?" veteran defensive end Jared Allen said of Williams. "For me that's absurd. It's absolutely absurd. It's just not what you do."

Added defensive tackle Fred Evans "You never want to see any enemy let alone one of your brothers go down like that and it was so ridiculous in a preseason game."

Aiello said the NFL's competition committee will study such plays to see if there's anything else they can do to prevent injuries. But that will not happen before or during the 2013 season.

Looney said Monday that he was "playing to the whistle" and that he didn't intend to target Williams' knee.

"I tried to find him after the game to apologize" Looney said "to let him know I'm not that kind of player who's trying to hurt guys and maliciously take violent hits at people."

An MRI on Monday showed that Williams does not have any ligament damage but that he does have a "significant bone contusion" and a posterior capsular strain.

Vikings coach Leslie Frazier said Tuesday that he's hopeful Williams can play in the season opener Sept. 8 against the Detroit Lions at Ford Field. But two knee specialists told the Pioneer Press on Monday that Williams could be sidelined three to six weeks if the bone bruise was in a weight-bearing location.

Frazier didn't specify the location of Williams' injury.

The uncertain status of Williams and the conservative approach being taken with first-round pick draft Sharrif Floyd who is recovering from a minor knee surgery challenges the depth of the Vikings' interior defensive line.

Asked about being thin at defensive tackle Frazier said "Well when you have a question mark regarding a potential hall of famer like Kevin Williams that creates some concern. He is one of the best to ever play the game at his position. We are all hoping he will be ready to go but it definitely creates some concern from a depth standpoint."

Evans said he and linemates like Letroy Guion will step up.

"It's not really that hard at all. In football at any level there's always the possibility of injury or ailment. We can't worry about it" Evans said. "We've been playing this game for a while so we know what to do."

Still Vikings defensive players went beyond a cursory outrage in support of a teammate. Allen who was fined $21000 last year for a blindside hit on Chicago Bears guard Lance Louis explained that he went high while Looney went low.

"I got fined ... something hefty because they said I launched and they said he was a defenseless player. I took it" Allen said. "But I had no ill intent. My problem with this play is intent. He ducked down to hit him in the knee. It was intent to hit him in the knee.

" If the league can't see that they can fine me for this because it's absurd."