Rashford, 19, burst onto the scene at Old Trafford under former manager Louis van Gaal.
However he initially struggled for regular game time following Jose Mourinho's arrival last summer.
The England international had to play second fiddle to Zlatan Ibrahimovic and was forced to operate out wide for much of the campaign.
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But Rashford finished the season strongly and ended up making 53 appearances in all competitions, scoring 11 goals in the process.
Mourinho even referred to the forward as one of his most trusted players in an interview earlier this year.
And he has now been singled out for praise by Park, who spent seven years as a United player between 2005 and 2012.
Asked by MUTV which young player at his old club had impressed him most, the South Korean star said: "Actually, yes [there is somebody]. Marcus Rashford has done really well.
"He had a great first season and then people had really high expectations but he showed his quality on the pitch in the second season.
"He’s improving with that pressure on him and that is quite impressive for me.
"If he can keep doing things like he is now, and progressing, he can be one of the best players."
