The 49ers released linebacker Brock Coyle on Thursday, the team announced. San Francisco also signed linebacker David Mayo to a two-year deal and announced linebacker Elijah Lee has signed his exclusive rights tender. 
Coyle later announced his retirement from football due to the back injury that cut his season short in 2018 [Twitter link].
Injuries are a part of this game and it is a risk all players willingly take when we step onto the field. Unfortunately, the injury I sustained last season is one that will prevent me from returning to the field again.
Coyle, 28, joined the 49ers in 2017 on a one-year deal and impressed, starting 10 games and appearing in all contests while registering a career-high 62 tackles. He signed a three-year deal in the ensuing offseason but only played in one game in 2018 due to the injury.
Mayo, 25, was a fifth-round pick by the Panthers out of Texas State in 2015. He has appeared in all but one regular season game in the last three seasons with Carolina, making four starts and logging a combined 35 tackles. While he didn’t see a ton of action on the defensive side of the ball, Mayo is a strong contributor on special teams.
Lee, 23, was a seventh-round pick by the Vikings in 2017. The 49ers signed the Kansas State product off Minnesota’s practice squad that same season and he has appeared in 30 of a possible 32 games in his career. In 2018, the linebacker made five starts and logged 65 tackles with a sack and forced fumble.