MANKATO, Minn. -- Though the addition of Madieu Williams was overshadowed by the headliner acquisition of Jared Allen, the Vikings were excited about the versatile safety they signed on the first day of free agency.

Given a six-year contract worth as much as $33 million, including nearly $13 million guaranteed, Williams left Cincinnati to join a Minnesota defense coming off a strong season but searching for upgrades to a few spots.

Though safeties in the Tampa Two scheme primarily play zone coverage, Williams is considered quick enough to play some man-to-man -- and allow fellow starter Darren Sharper more freedom to roam if he wants to.

Sharper, who has 53 career interceptions, always wants to. But he might have to wait awhile for that, because Williams has a nerve problem in his neck.

It could keep him out for up to six weeks, coach Brad Childress acknowledged after Tuesday's practice.

"I don't know. I'm not clairvoyant," said Childress, who has been reluctant to provide injury information during training camp, citing the irrelevancy of the preseason.

"It's just going to be ongoing here," Childress said. "He's treating, and he's frustrated as well, but he's got a great, great attitude."

Williams' condition didn't become public until he was held out of Friday's exhibition game against Seattle. Childress indicated he was hurt during a practice earlier in camp. Defensive coordinator Leslie Frazier said Monday "there's no reason to be alarmed at this point" based on what he's been told by trainer Eric Sugarman.

"From all indications, everyone feels great about Madieu getting back on the field and being 100 percent soon," agent Kenny Zuckerman said in an e-mail.

So, with Williams set to miss at least a game or two of the regular season, is rookie Tyrell Johnson ready?

"I think I earned a little bit of respect when I was out there Friday playing with them and made a few touchdown-saving tackles," said Johnson, the team's second-round draft pick. "That's how you earn the defense's respect, just by making plays."

The injury to Williams gave Johnson extended time in his first game.

"It was just good to see him out there with the lights on," Childress said. "He had to make a couple of tackles in the back end, which all you care about when it gets to you right there ... to get him on the ground, and he did a good job of doing that."

Johnson has missed practice this week, too, due to sore abdominal muscles. He said he'll play in Saturday's exhibition at Baltimore, however.

Two other safeties under scrutiny are Eric Frampton and Michael Boulware.

Boulware was on the rise with Seattle as a rookie and converted linebacker in 2004, but he lost his starting job in 2006; last year, he was relegated to special teams after a trade to Houston.

Boulware has been behind Frampton on the depth chart, but he intercepted a pass from Gus Frerotte during team drills in Tuesday's practice and returned it for a de facto touchdown. He said he's found the Vikings' scheme refreshing, because it doesn't require as much thinking. Staying focused was one of his downfalls with the Seahawks.

"My guard is still up. Can it be this easy? Can my responsibilities be this easy? That's the biggest thing: Just relaxing and playing," Boulware said.

Childress praised Boulware for playing faster, without as much "gear grinding or smoke coming out of his ears." The coach also noted Boulware's ability to communicate on the field.

Frampton, who joined the Vikings last October, has the same extroverted style. That serves a safety well.

"If you're talking, you know what you're doing. You just call it out," Frampton said. "I could imagine it makes the coaches a little bit more comfortable, but it makes me a little bit more comfortable calling it out and making sure everybody's on the same page."

Drafted by Oakland, Frampton spent five games with Detroit last fall before coming to Minnesota during a whirlwind rookie year. His primary value is on special teams, but his role could expand on defense.

"By the end of the year, I knew it pretty well," Frampton said. "This is a new year, and I can apply that."

Copyright 2008 by The Associated Press