There is a lively debate amongst England fans about who is the better playmaker out of the two young stars.
Leicester maverick Maddison was the first of the pair to win an England cap with his substitute appearance against Montenegro in November 2019.
The journey has been longer for Aston Villa captain Grealish, who was persuaded to switch allegiances from Ireland in 2015 by former England manager Roy Hodgson.
Grealish and Maddison battle for possession in 2019
Gareth Southgate finally gave Grealish his England debut against Denmark last month, with Maddison missing the squad altogether due to a calf problem.
The Three Lions boss will be watching both players keenly ahead of next summer's European Championship, especially with Ross Barkley, Mason Mount and Dele Alli also vying for an attacking midfielder spot.
Grealish might be the star man at the moment with Villa flying in the league, but according to Piper, who now works for BBC Radio 5 Leicester, Maddison has greater potential than his midfield rival.
"I watch [Maddison] week in and week out and he is tremendous," Piper told Tribalfootball.com.
"Everyone keeps bringing up Grealish vs Maddison, for me Maddison's ceiling is higher and I think now you're watching Grealish operate at about his ceiling.
"He's a brilliant player, don't get me wrong. But I think Maddison can go again and really take his game to that next level I think he's that good."
Maddison and Grealish were linked with Manchester United last season, but both opted to sign long-term contracts with their respective clubs.
Speaking after penning his new four-year deal in August, Maddison stated his belief that the club can regularly challenge the Premier League orthodoxy.
He said: "It's an incredibly exciting time to be a Leicester City player with so many positive things happening on and off the pitch and I'm delighted to be part of that."
"What we've achieved as a club this season is a huge step forward for us and I know there's so much more to come from this team.
"I've enjoyed every moment since joining Leicester City."
Matt Piper's autobiography, Out of the Darkness, is out now on Pitch Publishing, which you can purchase here.