Muldoon broke his right arm during the first half of Ireland's 66-28 loss to the All Blacks last weekend in New Plymouth.
He underwent surgery in an Auckland hospital on Monday and is due to see the specialist, who performed the operation, for an assessment before returning to Ireland later this week.
Ireland team manager Paul McNaughton said that Muldoon is looking at a lay-off of between 'three to four months' and compared the fracture to the wrist injury suffered by Gordon D'Arcy against Italy in the Six Nations two years ago.
Commenting on Muldoon's injury in a newspaper interview, Connacht team manager Tim Allnutt said: "It is a serious fracture and the doctors are saying it will take around three months to heal and another month after that before he can go into a match situation.
"It's a terrible blow for John as he had put such a huge effort in and was playing so well, but he'll bounce back from this."
The 27-year-old Muldoon made his debut for Ireland on last summer's tour to Canada and the USA.
Last Saturday's game marked his third Test cap and came on the back of a terrific campaign at provincial level, where he starred in Connacht's run through to the Amlin Challenge Cup semi-finals.