Posted on May 11
The versatile Smalling, regarded as one of the brightest prospects in English football, had been tipped for inclusion in Roy Hodgson's squad for his ability to offer options at right back and centre-back.
United manager Sir Alex Ferguson said a groin injury which flared up in last weekend's victory over Swansea was more serious than initially thought and meant he would be unavailable for England duty.
"Chris has suffered a bad injury," said Ferguson.
"It is a groin muscle injury and he will miss the European Championships.
"We are assessing what to do at the moment but it is a bad injury."
Ferguson meanwhile confirmed striker Danny Welbeck would be available for this summer's tournament despite an ankle knock that had ruled him out of this week's trip to Sunderland.
"He is still out just now but he should be fit for the Euros," Ferguson said.