Colin McCarthy is slated to start Sunday at middle linebacker against San Francisco with Moise Fokou recovering from a sprained knee. Patrick Bailey and Zaviar Gooden didn't play in Seattle because of injuries. If they aren't back, the Titans wouldn't have a healthy backup.
So they signed Zach Diles, who was with the team last year, to give themselves depth at linebacker. The move came at the expense of Preston, who was waived.
The Titans hope Preston doesn't get claimed off waivers and then they will have the opportunity to sign him to their practice squad and, perhaps, ultimately get him back on the 53-man roster.
For now, they had little choice but to take a chance on losing Preston.