MADISON, Wis. (AP) — Wisconsin athletic director Barry Alvarez is giving high praise to Chris Borland after the former Badgers linebacker decided to retire from the NFL following a promising rookie season.

The San Francisco 49ers have announced Borland's retirement without offering specifics. Wary of head trauma, Borland has said that he wanted to do what was best for his health in an interview with ESPN's "Outside the Lines,"

Borland left Wisconsin in 2013 after four decorated seasons. He holds the Big Ten record with 15 career forced fumbles, the second most in major college history.

Alvarez said Tuesday that Borland is one of the "most impressive young men I've come across in my many years involved in college athletics."

Current and former Wisconsin players have also expressed their support on social media.

"Bro honored to play with you and also you being a man by making the decision a lot of people wouldn't. Congrats 2 a gr8 career," Philadelphia Eagles safety Chris Maragos posted on Twitter. He was a Wisconsin senior in 2009 when Borland was a freshman.

"Happy and proud for (Borland), & thankful I got the opportunity to call him a teammate. Special athlete, but yet the best is yet to come..." Jaguars fullback Bradie Ewing, who finished his Badgers career in 2011, said on Twitter.

Borland was known as a relentless worker and fiery team leader at Wisconsin. He finished with 420 tackles, sixth on the Badgers career list.

"Knowing Chris, his decision to retire at this time was well thought out and made after much consultation with people he trusts," Alvarez said in a statement.

"He obviously feels that this is the best decision for him, personally," Alvarez added. "He will always be a part of the Badger family and we wish him the best in whatever his future may hold."