Chris Henry's omission from the squad to play South Africa last weekend raised a few eyebrows.
Ireland's team doctors put the headaches with which the forward was suffering down to migraines from a viral sickness but news came today that the issue is more serious than first anticipated.
It has now emerged that the Ulster flanker was actually suffering from a temporary blockage of a blood vessel in his brain.
A statement from the IRFU today said: "Chris Henry suffered some weakness on the morning of the South Africa game and a viral illness was suspected, he recovered quickly and the initial diagnosis was of severe migraine.
"Further tests however have shown he suffered a temporary blockage of a small blood vessel in his brain. He is at home now and is well but needs further investigation and specialist opinion."
