Steve Bruce signed McGinn from Hibernian early last season and he had a huge impact on the club, helping them to promotion via the play-offs.
And the Scot has gone to become a huge fans' favourite - as we as a massively popular member of the Villa squad.
But Grealish admitted: “I certainly didn’t know anything about Ginny [McGinn] before he came down here."
Villa's playmaker added in an interview with the Daily Record in Scotland: "I didn’t know how good he was going to become or how good he was when he first walked in the door at Villa.
“When he first signed, I’d just had a move to Tottenham fall through.
“Steve Bruce said to me, ‘things are going to take off here - we’ve got John McGinn coming in.
“No disrespect - but I’d never heard of John McGinn! I was thinking, he’s coming down from Scotland for about £2m...
“But from the day he walked through the door he blew me away with his attitude and ability. He has been a breath of fresh air for the whole team.
“That’s why he won the Manager’s Player, Players’ Player and Fans’ Player of the Year awards last season. He should have won our Goal of the Season as well, but somehow I won it!
“He’s brilliant and I love him.
“I’ve played with John and Callum (McGregor). They complement each other massively because they are not the same players.
“They are both left footed, similar ages. I’d say Callum is the more technical of the two, whereas Ginny is one of those players who is hard to explain because he gives so much to whatever team he plays for.
“Ginny has been my favourite player to play alongside in my whole career.
"Is he the best? I don’t know but he would be up there. He’s certainly my favourite.
“You know exactly what you are going to get week-in, week-out from Ginny. You know you are going to get hard work, you know you are going to get someone who will back you up, whatever you do.
“If anything, I think he’s underrated.