The Ireland flanker suffered a temporary occlusion of a small blood vessel in his brain on the eve of the game against South Africa at the Aviva Stadium a couple of weeks ago.

Henry is expected to make a full recovery and hopefully resume his career after, but he is unlikely to play again this season.

The 30-year-old Ulsterman, who has returned to his Belfast home, will continue to undergo specialist neurological assessment to determine the root cause of the problem which was confirmed by the IRFU yesterday.

There were suggestions he had suffered a serious illness, but the initial medical diagnosis pointed to a severe viral infection which had prompted a severe migraine. The IRFU confirmed the player requires more medical intervention to ascertain the full extent of the problem.

Heaslip said: “It’s never good hearing a player is out. All the players are thinking of him obviously and he’s got the best around looking after him.

“I don’t want to talk too much about it, because it would be unfair of me, it’s a private matter but we were just told he was unavailable.”

“Playing with him and against him over the past couple of years, he’s a nightmare to play against, and like every good seven, he has that ability in the dark arts to get in there and mess ball up, legally or illegally, whatever your viewpoint is.

“He is a great player, has serious work rate, I don’t think he gets enough credit for that, and it’s not great having a player like that unavailable for selection, so it’s a big loss.”