0318 GMT January 28, 2020
Courtois is on about £90,000 a week on a deal that lasts until 2019, though the 25-year-old is understood to want to at least double that, dailymail.co.uk reported.
Fellow Belgian Eden Hazard is on £200,000 – the same as David de Gea at Manchester United.
Chelsea is hopeful that it can come to an agreement ahead of the start of next season with Courtois due back in July for pre-season training.
Courtois won the Golden Glove with Chelsea last season as the side was crowned champion in Antonio Conte’s first season in the Premier League.
He has been linked with Real Madrid in the past although Zinedine Zidane appears to be more likely to sign the aforementioned De Gea or Milan's own contract rebel Gianluigi Donnarumma.
However, failure to extend his contract before the start of next season could set a spark should the Spanish champion fails to land its targets this summer.