He has reminded Manchester City counterpart Roberto Mancini of the Black Cats' record against his team after the Italian suggested Manchester United's run-in was not as difficult as his side's.
Mancini: "After the derby, United have two games which are not easy, but not difficult like us."
O'Neill: "It took me by surprise because I had to check that the teams they [United] have to play beat Manchester City, like Swansea and ourselves.
"He had obviously forgotten to check the fixtures list properly.
"I will remember it for the next four years. I don't have an email address for him, but I really thought about sending him one to tell him to keep an eye on what he says in the future.
"I don't know what his insinuation was.
"But if he had any idea about the league at all he would know that the integrity of the league is pretty good."