The attacking midfielder, who scored twice against Sunderland in the 3-0 win, has long-been linked with a move to the North East.
Maddison has a £2.5million release clause and the Black Cats were never going to spend that much on a player out of contract next summer.
Whether Sunderland make a move next summer, when he'd be a free agent, remains to be seen but his current chairman is confident his star player will remain for the entire season and hopefully beyond that.
Posting on Twitter, MacAnthony said: "Marcus will be a Posh player 100% for the whole of this season for sure.
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“No-one will pay the release fee for someone who only has six months left on his contract.
“When we spoke recently, I said ‘go have season of your life and write your own ticket’ and if that get us up then everybody wins.
“And I’d back myself to get him signed up for 46 games playing in the Championship as opposed to going to new club and having to prove himself etc to finally play in the Championship.”