San Francisco 49ers Chris Borland Retires after One Year, Fears Brain Injury

San Francisco 49ers Chris Borland has decided to quit after just one year in the league.

The 24-year-old linebacker, who was one of the NFL's top rookies this past season, stated that he feared for his mental health. Borland made his decision after discussing it with his family, friends, current and ex-teammates, and concussion experts.

"I just honestly want to do what's best for my health," Borland told "Outside the Lines" Monday. "From what I've researched and what I've experienced, I don't think it's worth the risk."

He added, "I feel largely the same, as sharp as I've ever been. For me, it's wanting to be proactive. I'm concerned that if you wait 'til you have symptoms, it's too late. ... There are a lot of unknowns. I can't claim that X will happen. I just want to live a long, healthy life, and I don't want to have any neurological diseases or die younger than I would otherwise."

According to ESPN.com, more than 70 former football players had some kind of neurological disease diagnosed after their deaths. These mental health problems, which have been linked to repeated hits to the head, include memory loss and depression.

Borland was expected to be a huge part of the 49ers defense next season. He replaced linebacker Patrick Willis last season when Willis was sidelined due to a toe injury. The 49ers have confirmed Borland's retirement.

"While unexpected, we certainly respect Chris' decision," team general manager Trent Baalke said. "From speaking with Chris, it was evident that he had put a great deal of thought into this decision. He was a consummate professional from day one and a very well-respected member of our team and community. Chris is a determined young man that overcame long odds in his journey to the NFL, and we are confident he will use the same approach to become very successful in his future endeavors. We will always consider him a 49er and wish him all the best."

His teammates and former teammates showed their support online:

"Shocked to hear the news about my dude Borland, but I totally understand his decision to retire," wrote 49ers linebacker Chase Thomas. "Much respect."

49ers cornerback Tramaine Brock said, "I understand but still shocked."

Russell Wilson, the Seattle Seahawks quarterback, wrote, "Pleasure playing with you, Chris Borland, and against you for the 49ers. Praying for you."

Borland, who has had two diagnosed concussions, stated that nothing can change his mind. He is the fourth NFL player aged 30 or younger to retire from the league this past week. The others included Willis, 30, Pittsburgh Steelers linebacker Jason Worilds, 27 and Tennessee Titans quarterback Jake Locker, 26.

In 14 games, eight of which were starts, Borland recorded 107 tackles and one sack.