Asked if he would compared his style to Henry, Butt added: "Yes. Blistering pace. When Marcus runs at you, you can't stop him.
"Until he gets his physicality about him he's going to find it very hard to play up against some of these centre-halves. It depends how the manager [Jose Mourinho] is going to play; if he plays a Michael Carrick, who can clip balls in for Marcus to run on to, then it's all different, he can run in behind all day."
He dropped into England's under-21s for Tuesday's game against Norway, and further underlined his potential with a hat trick on his debut at that level. It came on the back of his injury-time winner for United after coming off the bench at Hull before the international break.
Rashford has spent all of this season on the bench for United so far, following the arrival of Zlatan Ibrahimovic from PSG, though Butt thinks Mourinho will have to start the youngster if he continues to develop at such a fast pace.