United currently lead the Premier League by five points, although Arsenal have a game in hand and United are yet to travel to the Emirates this season, leaving the title race in the balance.
With the Red Devils in action at relegation-threatened West Ham this weekend, Nani insists they will not be taking the Hammers lightly.
“Our visit to West Ham is the sort of situation that decides titles,” he told The Sun.
"We are obliged to win if we want to be the champions. This month is so decisive and our challenge is to win every match, so as not to depend on others to obtain our objectives."
The Portuguese international is set to play a key role in the title race and the Champions League, but insists that despite facing Chelsea in the quarter-finals of Europe's elite competition next week they are currently looking no further than today’s game at Upton Park.
“No one in the dressing room is thinking about Chelsea yet - only West Ham.
"The real truth is every match between now and the end of the season is like a cup final. We can't give our rivals anything."