The striker picked up a knock in the Villans' pre-season friendly against Chicago Fire and is expected to be out for five to six weeks after a scan revealed damage to the medial ligament in his left knee.
Dunne has been sidelined by a groin injury, which the Villans claim was picked up during Euro 2012 and not treated by Republic of Ireland medics.
A club statement read: "Richard Dunne will also be out of action for six to eight weeks, having undergone a procedure on a groin injury which he sustained and was not dealt with during the European Championships."
Dunne played every single minute of the Boys in Green's disastrous campaign in Poland and Ukraine that saw them finish bottom of Group C with no points.
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