The optimistic followers of the 2008 Vikings are advised to have one major concern when their heroes play a second exhibition game tonight in Baltimore.

The play of Tarvaris Jackson? Certainly, further examples of his progress as a quarterback are worth monitoring as he stretches out his workload to the first half against the Ravens.

More life from the first-team defense? Again, it would be reassuring to see those much-ballyhooed defenders dominate the feeble Ravens offense, particularly after offering little resistance in their brief action against Seattle.

These are issues worth monitoring, but what matters tonight for the Vikings is that no one of importance gets escorted off the field with a leg bent at the knee, or sent to the locker room on an equipment cart.

There are four main factors for a football team: offense, defense, special teams and injuries.

And, injuries have the same ability to build momentum as do those other areas.

Associated Press, Star Tribune
Safety Madieu Williams, a free-agent signee for the Vikings, will miss up to six weeks because of a neck injury. He joins linebacker Heath Farwell and end Jayme Mitchell as key injured defensive players.

By all accounts, Brad Childress was as committed to nonviolence for three weeks in Mankato as is the prairie pacifist, St. John's John Gagliardi, when he gathers his Johnnies for preseason camp.

No matter.

The Vikings came to Mankato without starting defensive end Kenechi Udeze, lost for the season because of leukemia. They have lost three more significant players in the past three weeks: starting safety Madieu Williams, star special-teamer Heath Farwell and backup defensive end Jayme Mitchell.

Williams is the most significant absence. He has a neck problem. The Vikings have refused to identify the source of this injury. What's known is they gave $13 million guaranteed to a player with an injury history in Cincinnati, and now he has a malady in the worst possible location -- neck -- for an NFL safety.

If Williams turns out to be damaged goods, the Winter Park brain trust figures to declare abstinence when it comes to signing veteran safeties.

In 2006, the Vikings signed Tank Williams (injury history) and Dwight Smith (off-field issues). Williams missed 2006, played some last season and then was hurt again. Smith started 28 of 32 games in two seasons, mixing in an arrest for sex in a stairwell and an incident with police while parked in front of a downtown strip club.

Too bad Dewey wasn't around when the Love Boat sailed in the fall of 2005. He might've been wearing the captain's hat.

Smith signed with Detroit, where the headline could have read, "Losers sign loser." Williams signed with New England and suffered a possible career-ending knee injury in the exhibition opener.

The Vikings took a shot at another veteran safety -- Mike Doss -- last season. He was injured for half of the season.

They went big-bucks this time in signing Madieu Williams, who came with the highest recommendation of defensive coordinator Leslie Frazier. And now Williams has a bad neck, and all the Vikings have for a replacement is rookie Tyrell Johnson, a second-round draft choice from Arkansas State.

The eternal battle cry is, "Injuries are part of the NFL," but the addendum to that is, "If injuries become too much a part of it, they will ruin a season."

Go back to 2005. Mike Tice's team had backed into the playoffs a year earlier, then won a wild-card game at Green Bay. There was a modest degree of optimism entering the '05 season, even though Randy Moss had been traded.

And then: Running back Onterrio Smith was suspended for the season. Center Matt Birk missed the season to injury. Quarterback Daunte Culpepper missed the last nine games after finally showing signs of getting his act together. Udeze and special-teams ace Willie Offord missed most of the season. Another handful of defensive starters missed two or more games.

You look back at the injuries, along with the tight-fistedness of previous owner Red McCombs in compiling a roster, and Tice deserved Coach of the Year votes for the 9-7 record rather than to be fired.

The optimism the Purple Faithful is feeling right now remains legitimate, but there is a five-game start to the schedule to fret: road games at Green Bay, Tennessee and New Orleans, and home with Indianapolis and Carolina.

The Vikings figure to be underdogs in four of those games, and that's if this injury thing stops right now.

Patrick Reusse can be heard weekdays on AM-1500 KSTP at 6:45 and 7:45 a.m.and 4:40 p.m. • preusse@startribune.com