Manager Scott Servais said Diaz has been limited over the past couple of games due to back spasms, Greg Johns of MLB.com reports.
This helps explain why Diaz wasn't used in back-to-back close games against the Orioles. He was apparently available in a limited capacity Wednesday, so the issue doesn't appear to be anything overly serious. With an off-day Thursday, Diaz will likely be ready to go for the upcoming weekend series against the Athletics.