Cause for concern in Niners’ secondary

The 49ers released cornerback Chris Cook this week after a short stay with the team. At his best, Cook would have been a starter for the 49ers in 2015, but we have never seen Cook at his best for very long. He joins Perrish Cox and Chris Culliver as cornerbacks who were on the 49ers roster last year but are no longer with the team.

Going into camp, Tramaine Brock is a clear favorite for one of the outside cornerback spots. In 2013 Brock was excellent with five interceptions and nine passes defensed, but he missed nearly all of 2014. Now that Cook is gone, the competition for the other outside spot is down to Shareece Wright and Dontae Johnson.

While Wright is the favorite to start, we have liked Johnson more based on what we’ve seen so far. In 2014, Wright was our third-lowest-graded cornerback in coverage. He allowed an NFL Passer Rating of 95.5 when quarterbacks threw his way, and had 11 penalties called on him (tied for sixth-most among cornerbacks). Johnson played well as a rookie as a part-time player, but in the last three weeks he started, and in those games he allowed a troubling 204 receiving yards on 15 catches and two touchdowns.

Throw in the fact that slot cornerback Jimmie Ward allowed an NFL Passer Rating of 138.2 last year as a rookie, and there is reason to be concerned. It’s a young group of players who could improve, but they haven’t yet proven they can be effective on a defense that is trying to replace several key contributors.