The skipper believes the Scot, who signed from Hibernian last summer for £2.75million, has the potential to one day star in the Premier League and compared him to former Villa captain Fabian Delph.
McGinn put in another powerhouse performance as Villa came back to beat Rotherham 2-1 on Wednesday night, despite playing most of the match with 10 men.
Grealish said: “Ginny counts as two people and I don't mean the size of his head, either! Honestly, he is brilliant.
"There are so many players in our team at the moment who could play in the Premier League but a special mention must go to him.
“He has been unbelievable, easily the buy of the season. I absolutely adore playing alongside him.
“Even games like Wednesday when he didn't score or get an assist but you can just see the impact he has on games, driving us up the pitch.”
Grealish played alongside Delph in Villa’s run to the 2015 FA Cup final and he added: “I said to him the other day I am not sure who I would choose between him and Fabian.
“I loved playing with him when he was here and Ginny reminds me of him, the way they are both so eager to get the ball back and their work off the ball.
“But both are great with the ball at their feet too He has given us a massive boost.
“When he was suspended I think he needed a little rest because he had played pretty much every minute. He needed the rest and now he has come back in he is unbelievable.”
Villa boss Dean Smith is hopeful Kortney Hause will be fit for tomorrow’s showdown with play-off rivals Bristol City.
The on loan Wolves centre-back missed the win at Rotherham after sustaining the injury in last weekend’s victory at Sheffield Wednesday.
Villa, who are hunting an eighth straight league win for the first time since 1975, will be without the suspended Tyrone Mings.