The last victor outside of the superhuman pair is Kaka, the Brazilian playmaker who won the prize in 2007.
Ronaldo and Messi have won the award between them for the last 10 years.
Wales forward Gareth Bale and England striker Harry Kane are among the nominees for the 2018 Ballon d'Or, BBC Sport reports.
The Croatian had a stellar year, leading his country to an unlikely World Cup final while also winning a third-consecutive Champions League title.More news: Sotomayor on the Supreme Court: ‘We have to rise above partisanship’
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Modric's global team-mates Mario Mandzukic and Ivan Rakitic are also on the shortlist, as are Liverpool duo Mohamed Salah and Sadio Mane.
The ceremony to announce the victor will take place in Paris on 3 December, when a women's award will also be presented for the first time.
For the first time, a Ballon d'Or for women players will be awarded this year, with Champions League winners Lyon accounting for seven of the 15 nominees.
Cristiano Ronaldo headlines the latest batch of players to be announced as nominees for the 2018 Ballon d'Or by France football.
France internationals Amandine Henry, Amel Majri and Wendie Renard are joined on the list by Germany's Dzsenifer Marozsan, England's Lucy Bronze, Ada Hegerberg of Norway and Japan defender Saki Kumagai.
The award merged with the FIFA World Player of the Year prize from 2010-2015 to create the FIFA Ballon d'Or, but returned to France Football magazine in 2016 while FIFA established The Best awards.