The pundit said the lure of playing at Old Trafford would be an attractive option for the midfielder.
Speaking to Sky Sports' The Debate (h/t Matt Maltby of The Mirror), Murphy said the player would have little hesitation about joining the Red Devils:
"You cannot tell me there's a young English footballer at Leicester, no matter how well they are doing, who would turn down Manchester United. It's not going to happen.
"I am not a United fan but they still have the draw. To play at Old Trafford every week instead of Leicester, regardless of position, he is gone."
"If he is confident enough in his own ability, he will think he can take United into the top four next season."
The 23-year-old has seen his reputation explode in the past 12 months, and he's considered one of the most exciting players in the Premier League.
Maddison's creativity has helped his club up to second, and Brendan Rodgers has allowed the player addition responsibilities on the pitch.
The former Norwich City attacker has scored five and assisted three goals in 15 Premier League appearances, and his profile continues to grow.
United have seen an upturn in performances after Fred's improvement, and his partnership with Scott McTominay has been crucial for Ole Gunnar Solskjaer.
Paul Pogba's injury absence has hindered creativity, and the addition of Maddison would solve United's midfield challenges.
Solskjaer made three signings last summer, and United's squad might need further additions in January.
However, with Leicester riding high, it's unlikely Rodgers will be keen to do any business that sees outgoings from the King Power Stadium before the end of the campaign.