The 18-year-old striker has impressed in United's junior sides this season, scoring three times at Under-19 level and also finding the net regularly for the Under-21 team.
His breakthrough into the senior side, though, has surprised even the most optimistic of United supporters, with four goals in his first two games.
Having struck twice in a Europa League win over FC Midtjylland last Thursday, Rashford followed that up with two more in Sunday's 3-2 Premier League victory over Arsenal.
Manager Louis van Gaal is wary of asking the Manchester-born forward to take on too much responsibility too soon, but leaving him out against Watford may well prove impossible.
Even so, Van Gaal is urging caution.
"We have to wait and see with Marcus," he said. "He has only played two matches. It is about consistency. He has to show it in the third and the fourth and the fifth game.
"But what he has shown in the second match is already an improvement on the first and that is special."
Rashford is not the only young player to break into the United side in recent weeks.
Defenders Donald Love, Regan Poole and Timothy Fosu-Mensah have also been given debuts since the beginning of February, as have midfielders James Weir and Joe Riley.
To a certain degree, Van Gaal's hand has been forced by a long injury list.
Rashford was only given a chance because of a hamstring injury to Anthony Martial, with United short of options in attack as Wayne Rooney recovers from the knee injury that is set to keep him out until April.
Fosu-Mensah, meanwhile, was thrown on against Arsenal after Marcos Rojo injured his ankle, joining a casualty list that includes Matteo Darmian, Ashley Young, Bastian Schweinsteiger and Marouane Fellaini, among others.
The emergence of so many youngsters, though, has cheered up United supporters who have had little else to shout about this season.
It perhaps helps that they have come through at a time when their team has started winning again.
The victory over Arsenal was their third in a row in all competitions and has reignited hopes of qualification for next season's Champions League. United lie fifth, three points behind fourth-place Manchester City.
Watford manager Quique Sanchez Flores is hoping to take advantage of United's gruelling schedule of six games in 19 days, as well as the club's lengthy injury list.
"Sometimes when we plan for the match it's like we always need to be inside of the manager's head on the other team," he said.
"I don't know exactly how Van Gaal is thinking about the next match or what his focus will be. They have a lot of targets in this moment and play a lot of matches. For us it is an opportunity to have points.
"We know we are very competitive and we can go every single step to win. Now we have 37 points and we are happy."
The weekend 0-0 draw with Bournemouth left Watford comfortable in 10th place and effectively ended any lingering fears that they may get dragged down the table.
Flores may take advantage by resting Etienne Capoue after the midfielder was withdrawn against Bournemouth.
"Capoue is a very important player for us," the Spaniard said.
"He has played a lot of minutes this season. I felt he might be a bit tired. I felt he was not clear in the mind, he was not normal, but it is possible when a player plays a lot he is a bit tired."- AFP