San Francisco 49ers right tackle Anthony Davis has announced his retirement from the NFL.

Davis becomes the fourth key player to hang up his cleats from San Fran this season, with Chris Borland, Patrick Willis and Justin Smith also departing.

"After a few years of thought, I've decided it will be best for me to take a year or so away from the NFL," said the 25-year-old in a statement, according to the NFL's official website.

"This will be a time for me to allow my brain and body a chance to heal. I know many won't understand my decision, that's ok.

"I hope you too have the courage to live your life how you planned it when day dreaming to yourself growing up. Your life is your dream and you have the power to control that dream. Im simply doing what's best for my body as well as my mental health at this time in my life."

Given the wording of the tackle's statement, it is unclear whether Davis will take a temporary retirement or if he plans to leave the game for good.