SAN FRANCISCO » The San Francisco 49ers say linebacker Chris Borland is retiring.

Borland told ESPN’s "Outside the Lines" earlier Monday that he is retiring following his standout rookie season because of concerns about head trauma.

The 24-year-old Borland had a team-leading 108 tackles in his stellar rookie season, emerging as a punishing defender. He also had a sack and two interceptions.

He told "Outside the Lines" on Monday he wants to do "what’s best for my health."

This is yet another blow to the team that lost coach Jim Harbaugh after the season, then watched Frank Gore, Mike Iupati, Chris Culliver and Perrish Cox depart in free agency this past week.

Borland’s big announcement comes less than a week after five-time All Pro linebacker Patrick Willis walked away from football.