Five questions as the Vikings report to training camp

The wide-open competition along the line figures to be the most heated of the summer. Matt Kalil and Alex Boone are penciled in as starters on the left side. But there is uncertainty at center, right guard and right tackle. John Sullivan, who has returned to the field after two back surgeries in 2015, will try to reclaim the center job from Joe Berger. Brandon Fusco and Mike Harris will compete at right guard. And Andre Smith is the clear front-runner at right tackle after the sudden retirement of Phil Loadholt. There's probably a solid offensive line in there somewhere. It's up to new position coach Tony Sparano to find the best combination of players and coax better play out of them.

The Vikings took Treadwell, a big-bodied receiver from Mississippi, in the first round in the hope he will become third-year QB Teddy Bridgewater's go-to guy. But coach Mike Zimmer does not hand starting jobs to rookies just because they are high draft picks. So this spring Treadwell worked with the second-stringers while Charles Johnson was the first-team split end (and took advantage of the opportunity with strong showings in practices open to the media). Johnson presumably will open camp with the first team, but Treadwell will get snaps with Bridgewater, perhaps sooner rather than later, giving the rookie a chance to become the Week 1 starter at split end.

For the third consecutive summer, the Vikings enter training camp with little clarity when it comes to the strong safety position next to Smith. They brought back last year's starter, Andrew Sendejo, and signed Michael Griffin, who was released by the Tennessee Titans this winter, to a one-year deal. Those two veterans appear to be the leading candidates for that open job, but unproven youngsters Antone Exum, Anthony Harris and Jayron Kearse also are looking to get into the mix. Zimmer wants to see these safeties play tackle football in actual games before naming a starter, so he again could wait until the end of the preseason before officially picking a partner for Smith.

The Vikings return all 11 defensive starters from last season in addition to all of their key reserves. They also signed outside linebacker Emmanuel Lamur and drafted cornerback Mackensie Alexander in the second round. Lamur could challenge veteran Chad Greenway to start at weakside linebacker, but the job appears to be Greenway's to lose. Alexander will try to steal the nickel cornerback role from Captain Munnerlyn. And a pair of second-year players in cornerback Trae Waynes and defensive end Danielle Hunter will try to unseat Terence Newman and Brian Robison, the incumbents at their respective positions. No wonder Zimmer feels good about the depth on D.