Puel outlined some of the qualities he thought made Maguire of interest to United.
Its the opening day of a new Premiership season and Manchester united play host to Leicester.
Puel said: "We have had good speaking with Harry recently and with the chairman also and we can not change our things just before a game and just before the new season, it is not possible for us".
"I'm confident he's going to Manchester United, but only for a couple of hours with us", Puel joked with reporters.
"I am happy to keep Harry of course and all our best players".
'I am happy to keep Harry. We have to prepare for this season with good possibilities'. He is our best player. We need to continue and build some good momentum.
But as far as Leicester are concerned, Maguire is not for sale. It is not serious'.
The 21-year-old has signed a five-year contract at the King Power Stadium, subject to the deal being given global clearance.
Summer signing Jonny Evans, formerly of United, Nampalys Mendy and Demarai Gray (ankle) are also concerns.
"It's a difficulty but my first feeling was that it is incredible for this player to show their quality and it's good publicity for Leicester", said Puel, who feels Maguire now has the confidence that he belongs on the world stage.
The Premier League curtain-raiser against United is expected to mark the debuts of the Foxes other major signings of the summer in Jonny Evans and James Maddison with both having recovered from injury.