Talk about this Vikings roster being tougher to crack compared to recent seasons is warranted.

In Mike Zimmer's third season at the helm, an overhauled defense has gone from worst before his arrival to one of the league's best. That came with many personnel decisions from General Manager Rick Spielman that created an infusion of new talent, primarily via 28 draft picks in three years, with an exodus of mainstays (Jared Allen) and role players (Fred Evans, Jamarca Sanford) alike.

On defense especially, unproven players will have a tough time usurping a starting unit returning 97 percent of the snaps from a season ago. Their competitions will primarily take place for reserve roles and special teams — where coordinator Mike Priefer could look to take it easy with an injured Cordarrelle Patterson and does want to rest proven cogs like Marcus Sherels and Adam Thielen.

"We know what they can do," Priefer said. "We're going to try and keep them healthy and they're going to get reps on the offense and defense. I do want to take a look at a lot of the young guys."

Undrafted returners in Marken Michel, Troy Stoudermire and Terrell Sinkfield have been in the mix during training camp practices, joining Jerick McKinnon, Sherels and Thielen. That's not counting 21 other spots on the kickoff and return units, where players like sixth-round tight end David Morgan, German receiver Moritz Böhringer and seventh-round safety Jayron Kearse can further prove their worth.

That's how the bottom third of a NFL roster is selected.

"A lot of those decisions are personnel decisions and the recommendations I give to Rick Spielman and coach Zimmer," Priefer said. "I won't be able to give good answers to their questions if I don't see them on tape. We're going to use a lot of guys, I think last year in the first preseason game we used 60 different guys on special teams. We're going to take a look at a lot of guys."

Vikings players are off Tuesday. Vikings coaches will meet for a personnel meeting, set around an afternoon groundbreaking for the new team headquarters in Eagan.

They'll return to training camp Wednesday for six more practices before combined practices and the Aug. 12 preseason opener in Cincinnati.