Greenwood, 18, has been called into the England squad for the first time ahead of the Nations League games in Iceland and Denmark.
The teenage terror plundered 17 goals in his breakthrough season for United to establish himself as one of the brightest prospects in European football.
Three Lions captain Kane believes Greenwood is a special talent who has a huge future in the game.
The Tottenham hitman said: "Mason's been great. Since the first session we've had you can tell he's full of confidence as a player, trying to shoot and take people on. That's exactly what we want.
"He's done great for his club, in that period after the lockdown especially, and it's great to have him in the team.
"People use the phrase 'natural goalscorer'. You work on being in the right place at the right time but some of it's instinct as well.
"Watching him in the short time that he's been here, he has all different types of finishes, which shows he's a complete finisher."
On his England call-up by Gareth Southgate, Greenwood had said: "It's a dream come true. Playing for England is every young boy's dream.
"It's a privilege and I'm honoured to be selected because it's a good group of lads. I'm just happy to be here.
"I got the phone call, I was at home with my dad. I was over the moon, excited and just couldn't wait to be out there.
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"The manager rang me and told me about my selection as well as my season at United.
"My dad was buzzing for me. He's level-headed though so he kept me down early. It's a dream come true like I said before."
England face Iceland on Saturday.