EDEN PRAIRIE — The Minnesota Vikings announced Wednesday that cornerback Asher Allen has retired from football, a curious decision for a 24-year-old who was about to enter only his fourth NFL season.

Coach Leslie Frazier didn’t get into specifics of the conversation he had with Allen last week, but did say he was surprised by the decision by the former third-round draft pick, who would have been counted on to provide depth in the secondary this season.

“I didn’t see that coming,” Frazier said after the team held an optional practice. “Everybody has to make decisions that they think are best for them.”

Allen was drafted out of Georgia in 2009. He started 11 games in 2010, but struggled last season as part of the Vikings’ banged-up secondary. He had four interceptions in his career.

Allen suffered at least two concussions in his three years in the NFL, including one last season. Concussions have become a front-burner issue in professional football in recent years, with hundreds of former players suing the league alleging it turned a blind eye to the long-term effects that head injuries can have.

According to Frazier, Allen did not say whether it was related to injuries. The Associated Press left a message for Allen and his agent seeking comment.

“He will talk about it more at some point,” Frazier said. “He explained to me that this is something that he wanted to do and he had given it a lot of thought and that is what he wanted to do.”

Allen wasn’t expected to compete for a starting position this season with the Vikings, but the physical cornerback was being counted on to play some in nickel and dime packages, especially early while rookie Josh Robinson got up to speed.

Allen started 21 games in his three-year career, including nine starts as he filled in the for the injured Antoine Winfield and the suspended Chris Cook.

“We want depth, we want competition in the secondary and he definitely helped to provide that,” Frazier said. “But that opens up another spot and we’ll continue to comb the waiver wire. I know that (general manager) Rick (Spielman) and his staff are doing that and we’ll try to see what we’ll have by training camp.”