Romelu Lukaku would normally be the prefered option in the no.9 position for Jose Mourinho, but the Belgian forward has been out of form for the majority of this season.
The 'Red Devils' face their biggest test of the season in their next game when they play their city rivals away at the Etihad Stadium, with many tipping the 'Citizens' to win the tie.
Speaking to 'Sky Sports', Fletcher explained why Rashford would be an effective starter for Mourinho's men.
"I would like to see Rashford in. It’s a big dilemma (with Lukaku). There is a lot more fluidity with this front three. That would frighten Manchester City.
"They should treat the game as they did in the second half last season. They were brave and tried to get up the pitch. City will have long spells of possession so I would like to see pace in attacking areas."