Marcus will get opportunities in the first team because he's that good," Butt added. "Lee Sharpe was the best player in the country, as a youngster, but you couldn't hold Ryan Giggs back much longer.
"Here it's Zlatan Ibrahimovic, Wayne Rooney, Anthony Martial or whoever's up top. If Marcus keeps doing what he's doing with his pace and directness, it's impossible to hold him back."
Butt highlighted one young player that United hope can have a similar impact to Rashford.
"Angel Gomes is a young talented player we've massive hopes for," Butt said.
Gomes is a 16-year-old midfielder who plays as a No. 10, has featured for United at U18 level and has captained England's U16s.