The Vikings favor two tight end sets, and that requires depth at the position. They have five tight ends in camp, and injuries are beginning to take their toll. The remaining two weeks of the preseason will be important for the tight end position iand for backups trying to make the team.

TE John Carlson, who was brought in as a prized free agent during the offseason to give QB Christian Ponder more weapons to throw to, injured the MCL in his right knee on July 31. He has not returned to practice for three weeks. Coach Leslie Frazier hopes to get him back next week to do some work prior to the final preseason game, while Carlson said he will be back for the season opener.

He has missed plenty of valuable time building chemistry with his quarterback.

“He started to really come along,” Ponder said of Carlson before the injury. “He was new to this offense and he had to get comfortable. But especially in mini-camp, he was making plays--like in the two-minute drill where he made a catch in tight coverage. He has great hands; he’s a really smart guy--even though he went to Notre Dame (Ponder said jokingly). He is going to do well once he gets back.”

The other starting tight end, Kyle Rudolph, made an early exit Friday from the Bills game after he was sandwiched between two defenders. Rudolph went through the concussion protocol even though he thought it was more of an eardrum injury. He returned to practice on Monday, but the Vikings may want to be cautious with him the rest of the preseason.

That leaves two second-year tight ends, Allen Reisner and Mickey Shuler, and the rookie Rhett Ellison to bolster the unit. Reisner and Shuler are two pass-catching tight ends, and may be locked in a tight battle for a spot, while fourth-round draft pick Ellison (who has 3 catches for 25 yards in the two preseason games) has taken advantage of the extra first-team reps for a rookie.

“There’s definitely some more opportunities out there,” said Ellison. “I am just trying not to make mistakes—just play my role in the offense whenever I get a shot.”

Reisner was with the Vikings last season, bouncing on and off the practice squad, but he said he feels more comfortable.

“It is a lot easier to play knowing your assignment—before, you were just thinking about it in the huddle,” he said.

It may come down to who is the best blocker, since they can all catch the ball. They will need to fill the role vacated by the retired Jimmy Kleinsasser, who was one of the best blocking tight ends in the league. But if the injury bug continues, all three backups could find their way onto the roster.

For more Vikings news and notes, follow Joe Oberle on Twitter @CBSSportsNFLMIN.