United are expected to target a midfielder during this month's transfer window.
And Parker believes Leicester playmaker Maddison should be the priority.
He told bonuscodebets: "Jack Grealish is not consistent enough for me, to be honest. Whereas James Maddison has been playing a high level for a few months now. He has more experience in the league and is constantly being mentioned by players, managers and pundits as standing out this season."
"United don't need a player like him right now. They need someone who is going to be creative going forward and that is not something that Emre Can will provide."