Cook, 28, signed a one-year deal with the 49ers in March after playing just six games for San Francisco in 2014. He saw the field for just 48 snaps before a hamstring tear ended his season in Week 7.
With veterans Tramaine Brock and Shareece Wright penciled in to start alongside Jimmie Ward in the slot, the Niners also have Dontae Johnson, Marcus Cromartie and Leon McFadden at the position. The Sacramento Bee's Matt Barrows called 2014 fifth-rounder Keith Reaser the team's "most physically gifted" cornerback, giving Niners fans a name to watch this preseason.
Cook's future is hazy. The former second-round pick of the Vikings brings enviable size -- he's 6-foot-2 -- but his scant 29 starts over five seasons reveal a player who struggles to make the most of his build. He'll likely land one more shot as injuries pile up in secondaries across the league.