"Cian had ankle surgery on Wednesday, so he will be unavailable for about eight weeks, we hope," admitted O'Connor. "It was syndesmosis and they repaired that. He is doing good but he won't play for a while.
"The ankle sprains are becoming increasingly complicated. So that was probably longer than we would have liked obviously, but until you scan it you don't really know."
Healy was a late withdrawal for Leinster's 40-7 victory away to Northampton Saints last weekend. He injured his ankle in training and was replaced in the starting line-up by Jack McGrath.
The lay-off means the Clontarf man will miss the rest of the province's Heineken Cup pool matches, and he is unlikely to be fit for Ireland's Six Nations opener against Scotland on Sunday, February 2.