The 27-year-old secured a loan move to Barcelona, with a £30 million option to buy, and has since managed to rediscover some form.
Rashford has scored five goals and provided five assists across his 13 games across all competitions and is just behind Lamine Yamal (6) in terms of La Liga goal contributions for the club with five.
Former Man United and England forward Rooney admitted it was good to see the England international return to form but couldn’t help but be sad he wasn’t doing it with the Premier League giants.
“I'd much prefer to see him do that for Man United, if I'm honest," he said on the Wayne Rooney show.
"But no, listen… I don't think it was the easiest start, the first couple of games, and there were people talking about him, but he's got his head down, he's doing well, he's playing well, and for any young English player, and especially someone you know and you want to do well, it's great to see that.
"Listen, Marcus Rashford at his best is a top, top player and that's what we all want to see and just hope he stays settled and he keeps performing, keeps working and if he does that then I don't think there's any doubt about his ability.
"And you know what, I think fair play to Thomas Tuchel for bringing him in and playing him as well. Now Anthony Gordon has probably gone ahead of him a little bit in Tuchel’s plans, it looks like anyway, you don't know.
"But for bringing him in and playing him and picking him when maybe people didn't think he should. So I think fair play to Tuchel because that gives a player confidence as well.”