United are keen to become the first club in the history to be champions of England for four successive seasons.
They also have the chance to eclipse the overall record of 18 titles that Liverpool set in 1990.
Fletcher said: “The thought of winning the title again is our inspiration because no team has ever done in four times in a row.
“Doing things that haven’t been achieved before is what drives this club forward.
“People look at Manchester United and say we have no challenges left. But there are always challenges.
“When we win things we enjoy it, but in an instant it is time to go again.
“When we beat Villa in the Carling Cup Final there was no time to celebrate. It is all about winning trophies at the club so we don’t spend too much time celebrating what we achieve.
“There’s always another challenge waiting for Manchester United and when you’ve won one you start looking forward to the next one.”