The historic rivalry between the clubs would ensure some intense banter anyway, but the fact that 9,000 Leeds supporters are making the trip across the Pennines for the third-round tie will just increase the noise level even further.
As someone who has been involved in the biggest games in the most hostile environments, Fletcher, below, is experienced enough not to let the chants affect him.
"You do try and stay focused and treat it like any other game but the atmosphere brings it to a point where it can't happen," said Fletcher. "You realise how much it means to the fans because of bragging rights and past rivalries. The atmosphere builds up around the ground and you just sense it is not a normal match – and cup tie atmospheres tend to lend themselves to a more frenetic pace at the best of times."
Although he has been at United throughout his professional career, the fact Fletcher hails from Dalkeith gives him a certain detachment to what is a vicious rivalry. When he headed south, the Scotland skipper knew Manchester City and Liverpool would generate intense passions. Now he knows Leeds is the equal, if not worse.
"When I first came down here I was a little bit surprised," he said. "You hear about the rivalries with Liverpool and Manchester City but the Leeds one is just as big. The fans sing songs about it. Having played in a couple of the games I can testify as to how fierce it is."
After regaining form and momentum in post-Christmas hammerings of Hull and Wigan, the Red Devils are now gearing themselves up for a couple of famous cup encounters. Given Leeds' present status as a League One outfit, if Sir Alex Ferguson was going to give some of his senior players a rest, the first encounter would seem like a more obvious opportunity than Wednesday's Carling Cup semi-final first leg at Manchester City. Yet Ferguson has claimed he intends to keep changes to a minimum this weekend, then call back his youngsters for the City encounter. It also shows the respect United still hold for a Leeds outfit that has made giant strides under new boss Simon Grayson.
"You have to be wary of Leeds," because they are in such good form," said Fletcher. "They look like they are going to be promoted. I have been watching Leeds and they have been performing well."
Well enough to let their supporters at least harbour some hopes that the first meeting with the old enemy in six years can end in a first Old Trafford win since 1981. Veteran trio Gary Neville, Paul Scholes and Ryan Giggs are primed to stop them, although Fletcher feels United's first task will be to curb the enthusiasm and confidence of a side that has become used to winning, even if it is at a lower level.
"Why not come and have a go?" said Fletcher. "They will want to cause an upset and they will certainly be full of confidence, no matter what league they are in. It will give them a nothing-to-lose attitude.
"There is a history to this fixture which, however briefly, is going to be rekindled.
The result is important and we will need to be on top of our game because Leeds are a very physical and strong side, who can play some good stuff."