Vikings cornerback Asher Allen, just 24 and three years into his NFL career, has decided to retire, coach Leslie Fraizer announced during the second day of the team's Organized Team Activity.

"I'm surprised; I didn't see that coming," Frazier said. "But everybody has to make decisions that are best for them."

Allen told Frazier about his decision last Thursday in Frazier's Winter Park office. Frazier said Allen didn't mention health concerns as a reason for his decision. Allen has had concussions before, including one against the Saints last December. He missed the next game because of the injury.

As concussions and their potential for long-term cognitive complications have become a hot-button issue in the NFL, more players are retiring in their prime rather than risk further injury.  

"He'll talk about it more at some point," Frazier said of Allen. "He explained to me that this is something he wanted to do and has given it a lot of thought."

Allen was the team's third-round pick in 2009. He started nine of 12 games last season, finishing his career with 134 tackles, four interceptions and 11 passes defensed.

Allen went into last season as someone who might not make the team. But he eventually became the team's top corner after injuries, ineffective play and the legal woes of Chris Cook devastated the position.

The Vikings drafted two corners and added free agents Chris Carr and Zack Bowman during the offseason.

"You got to keep looking [for corners], like we would even if [Allen] were here," Frazier said. "You need to create competition and continue to upgrade that position. So that's what we'll do. We want depth. We want competition in the secondary. He definitely helped to provide that. But that opens up another spot, and we'll continue to comb the waiver wire.

"[Allen] would have been one of the corners fighting for a spot, like the other corners. But his experience would have helped us. But he's made a decision he felt was best for his family and you have to respect that."

The only other players not at Wednesday's OTA were linebacker Chad Greenway and defensive end Jared Allen. Greenway is tending to a family emergency. Allen might show up next week, Frazier said. OTAs are not mandatory.

Other than receiver Percy Harvin (shoulder surgery) and running back Adrian Peterson (knee), center John Sullivan was the only other veteran that didn't practice. He has a left leg injury that's not believed to be serious.