Sir Alex Ferguson insists United are pushed to the limits in every Barclays Premier League match and expects the trend to continue during the run-in.
Manchester City boss Roberto Mancini stirred some controversy ahead of the derby by claiming that the Reds have been given an easy ride in racking up a commanding lead in the table.
Although the competitive nature of most of United's matches this term would indicate otherwise, Mancini said: "No-one plays well against United because they only play with fear. Every team that plays against United plays very soft because they think this game is difficult, that they can't beat them."
However, Sir Alex has responded by emphasising the honesty of the English game and knows Stoke City and West Ham look certain to push the Reds all the way in the next two fixtures.
"I think that's absolute nonsense, I really do," countered the boss. "There are a lot of games I've watched this season, teams like City, and I've said to myself 'are they trying?' - of course they're trying.
"The English game is the most honest in the world, I think we all recognise that, and it has been for many, many years. And also you've got 3,000 fans following you away. There's no way any team could come to Old Trafford and not do their best. That also applies itself to the Etihad, Stamford Bridge, the Emirates or Anfield. They all do their best because that's the nature of the English game.
"So it's absolute nonsense what he [Mancini] said. He was maybe looking for a bit of self-sympathy or something like that. But it's nonsense.