The 22-year-old midfielder, who is on a season-long loan from West Ham, suffered adislocated shoulder during the Addicks' 2-0 win against Walsall in League One on Tuesday night.
A club statement read:
Head of medical services Alastair Thrush confirmed that as a result of the injury Cullen underwent keyhole surgery today (Thursday) to repair the shoulder and it is anticipated this will keep him out of action for the next 10-12 weeks
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