Scans revealed that D'Arcy had broken his arm in seven places with the injury requiring the insertion of a six inch titanium plate in his forearm.
But the Wexford man, who had been hoping to return for Leinster's Magners League title run-in, had to go under the knife again last Friday as one of the breaks had not healed sufficiently.
He had a sliver of bone from his elbow grafted to the damaged area in his arm, meaning he will be sidelined and require treatment for another month and will not return to contact work until Leinster's pre-season training regime begins.
The Ireland squad for their summer schedule of games is due to be confirmed in the coming days.