The Slovakian reportedly takes home €5 million (€4.47m) per season, though Cyclingnews has been informed that the real figure is still higher at €5.5m (£4.92m).
The figures come from a report by French newspaper L'Equipe, which published a list of the 20 highest earning riders in the world.
Four-time Tour de France winner Chris Froome is second at €4.5m (£4.02m), while his Team Ineos teammates Geraint Thomas and Egan Bernal are third and fifth at €3.5 million (£3.13m) and €2.7 million (£2.41m)
Two further Team Ineos riders feature in the top 20, with Michał Kwiatkowski in seventh place and the team's new signing, Giro d'Italia champion Richard Carapaz in tenth, both bringing home over €2m (£1.79m).
L'Equipe suggest the British team's budget for 2020 is a massive €45m (£40.2m), up almost €20m since the 2015 season and almost tripling the team's budget during their first season, 2010.
Julian Alaphilippe is predictably the biggest earner at the sport's other super team, Deceuninck-QuickStep. The Frenchman – who last year won Milan-San Remo, La Flèche Wallone, Strade Bianche, two Tour de France stages and enjoyed two weeks in yellow – lies just below Kwiatkowski, earning a reported €2.3 million (£1.90m)
The list is dominated by Grand Tour stars, with 12 filling out the ranking and Astana's Miguel Ángel López taking the 20th place spot at a reported €1.5m (£1.34m).
Perhaps surprisingly, given the number of wins they bring in year-on-year, only two sprinters feature – Fernando Gaviria on €1.8m (£1.61m), Elia Viviani on €1.5m at his new team, Cofidis.
Slovenian wonderkid Tadej Pogačar is the youngest rider among cycling's top earners.
The 21-year-old isn't on L'Equipe's list but Cyclingnews understands that he's already taking home €2m a season after his stunning neo-pro season for UAE Team Emirates last year and agreeing a new contract with UAE Team Emirates that last until 2024. Last year Pogačar won the Tour of California and three stages of the Vuelta a España en route to third overall at his debut Grand Tour.
Read on for the full list, amended with the information gleaned by Cyclingnews.
The highest earning riders of 2020
1. Peter Sagan (Bora-Hansgrohe) €5.5m
2. Chris Froome (Team Ineos) €4.5m
3. Geraint Thomas (Team Ineos) €3.5m
4. Vincenzo Nibali (Trek-Segafredo) €3m
5. Egan Bernal (Team Ineos) €2.7m
6. Fabio Aru (UAE Team Emirates) €2.6m
7. Michał Kwiatkowski (Team Ineos) €2.5m
8. Julian Alaphilippe (Deceuninck-QuickStep) €2.3m
9. Alejandro Valverde (Movistar) €2.2m
10. Richard Carapaz (Team Ineos) €2.1m
11. Thibaut Pinot (Groupama-FDJ) €2m
12. Primož Roglič (Team Jumbo-Visma) €2m
13. Tadej Pogačar (UAE Team Emirates) €2m
14. Nairo Quintana (Arkéa-Samsic) €1.9m
15. Tom Dumoulin (Team Jumbo-Visma) €1.8m
16. Fernando Gaviria (UAE Team Emirates) €1.8m
17. Romain Bardet (Groupama-FDJ) €1.7m
18. Greg Van Avermaet (CCC Team) €1.6m
19. Elia Viviani (Cofidis) €1.5m
20. Miguel Ángel López (Astana Pro Team) €1.5m