Adam Johnson out for three months
"I think we have lost Adam Johnson for three months," manager Roberto Mancini told the club website after the 1-1 draw at League One County.
"It's very unlucky. We don't have a player like Adam."
Johnson is likely to miss next month's Europa League last-32 tie against Greek club Aris Salonika and England's Euro 2012 qualifier against Wales in late March.