The 49ers plan to sign safety Tracy Walker, Matt Barrows of TheAthletic.com reports.
Walker, 29, worked out of the team Wednesday.
San Francisco, which cut safety Erik Harris this week, looked at veteran safeties this spring with Rayshawn Jenkins and Julian Blackmon among those who visited.
The Lions made Walker a third-round pick in 2018, and he started 43 games for them, including six last season.
He has totaled 398 tackles, three interceptions, 23 pass breakups and two forced fumbles in his career.