The Red Devils are believed to be targeting a central defender and Maguire is reportedly one of their targets along with Toby Alderweireld and Yerry Mina.
However, the Foxes boss says it's vital the club does not lose their best players before the transfer window closes for Premier League sides on Thursday.
"It's a good thing for Leicester to keep our valuable players, like Maguire, [Jamie] Vardy, [Wilfred] Ndidi - all these are very good players for us," Puel told Sky Sports News.
"It's important to keep them and have a good ambition for the next season.
"I can understand some speculation about our players because we have good players with good attributes, who are interesting perhaps for the future of other teams.
"But I am happy to keep them and to start, I hope, a great season."