Leinster coach Matt O'Connor has described as "a nightmare" the news that Sean O'Brien is out for up to six months.

The Carlow man is to have shoulder reconstruction surgery tomorrow.

O'Brien will miss all of Leinster's Champions Cup pool stage games, and much like Cian Healy will face a race to be fit for Ireland's Six Nations campaign.

However, O'Connor is adamant that the Tullow Tank will return as strong as ever.

"The shoulder will be as good as new. So he's looking at the upsides. Everyone is very disappointed for him and for the group personally. It's part and parcel of what we do everyday. He's upbeat and positive and just wants to get well and play again," said O'Connor.