Broken foot rules Smalling out for month
Smalling, 21, was absent from United's 1-0 victory over Everton on Saturday, with Ferguson revealing the extent of the problem after the match at Goodison Park.
"Smalling has a small fracture on his foot," Ferguson told MUTV. "I think he'll be out for a month and it's unfortunate that one.''
The England defender's lay-off means he will miss November's friendly internationals against Spain and Sweden, as well as United's next two Champions League clashes with Otelul Galati and Benfica, and Premier League fixtures against Sunderland, Swansea and potentially Newcastle United on November 26.