Palace have endured a mixed start to the 2026/27 Premier League season under new boss Pierre Sage with Mateta making just one top-flight appearance.
The France international remains in a dispute with Palace over claims the final year of his contract at the club is invalid and FIFA have been informed of his stance.
Mateta joined Palace on an initial 18-month loan, before making the move permanent and signing a four-and-a-half-year deal - including an option to extend by a further 12 months - in January 2022.
Palace activated that option in 2024, meaning his present contract will expire at the end of the current season.
However, this was disputed by Mateta's representatives over the summer, with United reportedly expressing an interest in the 29-year-old hitman, who has bagged double figures for goals in each of the last three Premier League seasons.
The Red Devils were unable to persuade Palace over a sale before the September deadline, but they will try again in January, and the Eagles could be forced to reduce their previous £35M asking price.
Palace have made a habit of selling players in the January market in recent seasons - if they opt against extending a contract beyond six more months - and United could test the water with a £20M bid.