Scans have revealed that the 25-year-old suffered a stress fracture during the 3-1 defeat against Wolves, and he is expected to be out-of-action for a month to six weeks.
Hughes has been in scintilating form for The Blues so far this season, scoring six goals in his 13 appearances to date.
His loss will undoubtedly compound the blow dealt by the loss of manager Trevor Francis on Sunday as The Blues look to halt a streak of six games without a win.
