The future of Kevin-Prince Boateng at AC Milan is again in doubt.Tuttosport says the attacking midfielder is upset with Milan not coming good on a promise last season over a contract upgrade.

Milan vice-president Adriano Galliani has told Boateng's representatives to forget about an increase from €2.3 million-a-year to €4 million-a-year.

The Ghana international was linked with Manchester United and Real Madrid earlier this season, while Bayern Munich are also keen.