Always a maverick, the American actor said he had been watching English football since the Eighties and predicted a "great game" between the top two.
Defeat for City would open up a six-point gap at the top of the table, which would be difficult to close against an in-form United.
"This is the first game that I've seen in England," Tom said on Sky Sports 1.
"I've been following it since the Eighties so I'm just excited that I'm able to be here."
The Jerry Maguire actor is friends with David Beckham and he revealed the former England captain had sent him a message ahead of the game.
"He wishes he was here. I got an email from him, he's jealous that I'm here," Tom added.
Apocalypse Now actor Robert Duvall was also at the game, but appeared to be a little rusty on the rules.
He said: "Will there be a shootout today? No. If it's a tie? No."