Seamus Coleman suffered a season ending leg break in the Republic of Ireland's 0-0 draw with Wales at the Aviva Stadium on Friday night.
The Everton defender crumbled under a reckless challenge from Neil Taylor.
"Obviously it's a real blow to him," manager Martin O'Neill told the press after the game.
"He was having the season of a lifetime at club level and is such a big player for us. He's a great captain and a great character.
"It's a big, big loss. A big loss to Everton. A big loss to us. He'll fight back I hope, but it puts things in perspective.
Wales were fortunate to finish with 10 men, Gareth Bale could've seen red for a studs up challenge on John O'Shea.
Former German midfielder Didi Hamann described the incident as cowardly and said the Sunderland man was lucky to escape unscathed.
O'Neill refused to wade into the row having not properly watched replays of the challenge:
"I've been rushing around since that, lads are telling me that that could have been a red card as well.
"I've not seen it. I've not even seen Seamus' tackle. I've been told that it's not great and that even the television went without showing a replay of the tackle."