Rashford netted twice in United's 5-2 win over Los Angeles Galaxy on Saturday night, with the 19-year-old producing two clinical finishes as the Red Devils comfortably overcame the MLS outfit.
Mourinho has hinted that he will look to use the England international as a centre-forward during the 2017-18 campaign based on the player's "evolution".
"It's just the natural evolution of the kid. An accumulation of minutes on the pitch. You change your body when you're a young kid, he's already taller than when I arrived 13 months ago, he's three centimetres taller and he put some muscle on but without any kind of specific work because his speed is the most important quality," Mourinho told reporters.
"Last season in this period everyone was saying it would be difficult for me to play him but he was one of the top appearance-makers of the team last season which is good for his evolution. He played in the Europa League, important matches, and he's learning a lot.
"He's a great pro, has a great attitude and last season he maybe was not scoring a lot of goals and missing some chances but it was not a drama because that's part of the evolution. We know he is going to score more goals than last season."