Welcome to the most important week of the summer.

Returning to Winter Park for a 1 p.m. practice today, the Vikings have reached the part of their preseason where more than baby steps are required to keep the pace.

Coach Leslie Frazier will treat this week more like he would a regular-season game. Practices will have a regular-season tempo, there will be specific game-planning for the Cowboys, and the starters will play into the second half on Saturday night at Mall of America Field. How long they play hasn't been determined, but coaches always mark the third preseason game as the one in which starters get reacquainted with returning to the field for the second half.

As far as baby steps to get to this point, the Vikings deserve a passing grade, all things considered. The defense was stifling in Saturday night's 20-7 win at Seattle, while the offense showed some rhythm after a slow start. Yes, the offense still hasn't scored a touchdown, but that 81-yard drive from inside their 1-yard line was impressive, especially considering it came without Percy Harvin (ribs) and Visanthe Shiancoe (hamstring), two major parts of a new offense still taking its baby steps.

Possibly the most unexpected observation to this point is how comfortable new quarterback Donovan McNabb has looked with a little more than two weeks in the offense. He's been decisive, sharp on the short and intermediate passes, threw a nice longer pass to Michael Jenkins and has shown he still can move around in the pocket.

So as we head into the big-boy steps part of the preseason, I wouldn't put McNabb among the top five concerns at this point. Here are my top five:

1, The offensive line.

Most coaches want their starting five in place by the third preseason game. The Vikings are unsettled up front, to say the least. They still don't know who their right guard is. Their left tackle looks like a guard and made a major mistake that gave Seahawks DE Raheem Brock an open path to McNabb. That can't happen. Not to a 34-year-old QB who hasn't survived all 16 games since 2004. The O-line is easily the biggest concern on this team.

2. The third cornerback.

The backup corner that's turned more heads this summer than any other is Marcus Sherels. That's good for the undrafted ex-Gopher, but he's the No. 6 corner on the team. He isn't going to move ahead of Chris Cook or Asher Allen, two young players the Vikings have a lot more invested in. Cook especially needs to start playing like a second-round draft pick. Or like he did last season before knee injuries derailed his career. He has it in him. In this division, the Vikings hope he relocates that ability in a hurry.

3. Strong safety.

The seemingly never-ending battle between preferred candidate Tyrell Johnson and Jamarca Sanford trudges on. Sanford started the preseason opener. Johnson started the second game. Whoever starts this week has the inside track for the regular-season opener. Rookie Mistral Raymond is a possibility. He would play free safety and Husain Abdullah would move to strong. The Vikings probably don't want to show Philip Rivers a rookie free safety on Sept. 11. The good news is there's nowhere to go but up from the Vikings' safety play in recent years.

4. The receivers.

Harvin, Bernard Berrian and Jenkins are the starters. Greg Camarillo probably is the fourth receiver (and second slot guy in four-wide sets). The fifth receiver could be the winner from a pool of interesting prospects. Devin Aromashodu would get my tentative vote. Harvin is explosive, but not a No. 1 receiver that can line up wide and present a physical mismatch. Jenkins has the size and deceptive speed, but he's never proven to be that No. 1 guy. And one wonders if Berrian, the split end, can be a deep threat if the offensive line can't give McNabb the time needed to throw deep. And what happens to Berrian's attitude if he's not a big part of the offense?

5. Injuries.

This is the week that Shiancoe, Harvin, Camarillo and others need to be on the field. It will be the only chance to play extended minutes as full units before the regular season begins. That's especially important for a brand new offense that's going to have to score touchdowns to keep up with the Chargers in San Diego. There needs to be a test run with a full complement of players.