San Francisco 49ers linebacker Chris Borland told Outside the Lines on Monday that he is retiring due to concerns over “the long-term effects of repetitive head trauma.”

According to ESPN, the 24-year-old told the 49ers of his decision on Friday. Borland said he first began to think about the possibility of retiring early during training camp last season. The rookie said he thinks he sustained a concussion, but played through it, partly because he wanted to make the team.

From ESPN:

Last week, linebacker Patrick Willis retired because he thought the injuries he had sustained while playing football would keep him from playing at an “elite” level and he was worried about the quality of his life after football. Borland told ESPN that his former teammate’s decision did not play a role in his retirement.

In a statement on Monday, 49ers general manager Trent Baalke said Borland’s decision was unexpected.

Borland told ESPN that he plans to go back to school to pursue a career in sports management. Borland has a bachelor’s degree in history from the University of Wisconsin.

ESPN notes that Borland is the fourth NFL player under the age of 30 to decide to retire in the past week.

This article originally appeared on SI.com

Contact us at editors@time.com.

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