The Black Cats beat Reading 3-0 during the week to move up to 15th in the Premier League table, and the Northern Irishman is hopeful his side can continue their good form at Old Trafford.
“The players have always been in decent spirits, but the midweek result has given us a boost and hopefully we can continue that over the Christmas and New Year,” he told the club’s official website.
“We’ve got a set of games coming up now which are particularly difficult. We go to Old Trafford with Manchester United a number of points clear at the top, so it’s a difficult game for us.
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Despite their hectic schedule over the holiday period - which includes clashes with Manchester City, Tottenham and Liverpool - O’Neill is keen to take each game as it comes.
He added: “I don’t think we can look that far forward. Bigger teams than us can perhaps plan a set of games, but we’re not in that position.
“We must treat each game on its merits, do our very best and try to win – it really is as simple of that.
“The next game will then take care of itself, one way or the other.”
O’Neill is the only manager in history to have tasted victory at Old Trafford with two different clubs, but says that is irrelevant this time around.
“These are different times now,” he said. “We’ve a real battle on but as I’ve said we can go there with some confidence.
“We must play with some sort of freedom. You have to compete every single week in this league. [The players] must go and play.”