Shaw withdrew from Sam Allardyce's England squad for the Slovakia World Cup qualifier as a precaution, after also missing training on Saturday
Allardyce said: “It's a slight problem with the leg. A little ache, muscular.
“With what he's been through, we didn't want to take a chance. It's the calf where the break was.
"He's done exceptionally well given the games he's played, but he didn't feel comfortable so the wise thing to do was send him back to United.
“He wasn't starting (against Slovakia) anyway. I'd be surprised if he wasn't okay for United's next game."