The Manchester United legend has agreed to become O'Neill's No2 with Ireland.
O'Neill revealed his astonishment at his availability.
He said: "I am. I know that he feels things didn't go very well at Ipswich for him.
"I think sometimes it's forgotten as well that in his first season, he actually got Sunderland promoted and did very well. Some of those things get lost in time and people want to forget that.
"But I think I was surprised that he hadn't had another opportunity, that somebody wouldn't have taken a chance with him.
"But who knows what might happen here? He's here, he is focused on it. He wants to do it and I think you will find tomorrow that he is especially ready for it."
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