Robertson had been listed on the travel roster for Thursday against the Cardinals in Jupiter, Fla., but Girardi told the YES Network that Robertson will not pitch in that game.
"It's not soreness," Robertson said. "Have you ever slept on your side and woke up and your shoulder didn't feel right? That's basically what it felt like."
General manager Brian Cashman had termed Robertson's situation as a "low-level concern," but the right-hander said it should be considered no concern at all.
"If it's the regular season, I'm pitching right through it," Robertson said. "I wouldn't even think twice about it. I've pitched on worse days."
Bryan Hoch is a reporter for MLB.com. Follow him on Twitter @bryanhoch and read his MLBlog, Bombers Beat. This story was not subject to the approval of Major League Baseball or its clubs.