The former Arsenal striker completed his controversial move to Old Trafford yesterday.
Speaking with talkSPORT, Schmeichel warned title rivals Manchester City: "It's a complete game-changer. An absolute game-changer. United and City were neck and neck over who would win the Premier League this season but it has now swung in our [United's] favour.
"We have to go out there and perform and produce the results but, with a player like that in the squad, everybody is going to get a lift from that and everybody is going to up their game.
"It is one player that everybody in the world that have ambitions in football have been trying to sign. He came to us and I'm very, very happy."