According to the Cycling Weekly website, the Russian businessman and owner of team Tinkoff-Saxo, home of Contador, said that the four can divide the money - €250,000 each - or put it all up for best placed rider.
Contador already said that he will race the 2015 Giro d’Italia and Tour de France. He has not yet confirmed if he will return to defend his 2014 Vuelta a España title.
After winning the 2014 Giro, Colombian Quintana said that he will skip the Giro to try to win the Tour. He won the white jersey of best young riders and placed second overall in 2013 behind Froome.
Froome and Nibali have yet to announce their plans for 2015, but both riders are expected to focus on the Tour.
Italian Marco Pantani was the last man to win the Giro d'Italia and the Tour de France in the same season in 1998.
However, no rider has added the Vuelta to win all three in the same season.