The winner will be announced in Monaco on August 29 during the draw for the 2019-20 Champions League group stage, Efe news reported.
Barcelona star Messi, who won the 2018-19 La Liga crown with the Catalan side, was the top goalscorer in last season's Champions League with 12 strikes.
Ronaldo won the top-scorer's trophy in the inaugural UEFA Nations League finals which Portugal won, besides helping Juventus win the Serie A title last season.
Liverpool's Van Dijk helped shore up his side's defence as it finished a close second in the Premier League before winning the Champions League.
Real Madrid star Luka Modric of Croatia won the award last year.
The midfielder won after a jury made of 80 coaches from clubs taking part in the Champions League and the Europa League, as well as 55 journalists from each of UEFA's 55 member associations selected by the European Sports Media (ESM) group voted for him.
Apart from Messi, Ronaldo and van Dijk, the other seven players in the fray are:
* Alisson Becker (Brazil/Liverpool) 57 points<br>* Sadio Mane (Senegal/Liverpool) 51 points<br>* Mohamed Salah (Egypt/Liverpool) 49 points<br>* Eden Hazard (Belgium/Real Madrid) 38 points<br>* Matthijs de Ligt (Netherlands/Juventus) 27 points<br>* Frenkie de Jong (Netherlands/Barcelona) 27 points<br>* Raheem Sterling (England/Manchester City) 12 points.