Disgusting tackle but his explanation is amusing.
https://www.theguardian.com/football/2014/oct/06/roy-keane-alf-inge-haaland-book
However, Keane also goes on to say in his new book, The Second Half, that he has never regretted slamming his studs into the knee of the Manchester City player. Haaland, he says, "pissed me off, shooting his mouth off. He was an absolute prick to play against. Niggling, sneaky. I did want to nail him and let him know what was happening. I wanted to hurt him and stand over him and go: 'Take that, you cunt.' I don't regret that. But I had no wish to injure him.
"It was action; it was football. It was dog eats dog. I've kicked lots of players and I know the difference between hurting somebody and injuring somebody. I didn't go to injure Haaland. When you play sport, you know how to injure somebody.
"There was no premeditation. I'd played against Haaland three or four times between the game against Leeds, in 1997, when I injured my cruciate and the game when I tackled him, in 2001, when he was playing for Manchester City. If I'd been this madman out for revenge, why would I have waited years for an opportunity to injure him?
More at the link.