Horacio Zeballos Jr. is an Argentine professional tennis player. He reached a career-high doubles ranking of world No. 1 on 6 May 2024, and a singles ranking of No. 39 on 4 March 2013. In doubles, he has reached the men's doubles finals at the 2019 US Open and at Wimbledon in 2021 and 2023 alongside Marcel Granollers. In singles, he has reached the fourth round at the French Open, doing so in 2017.

The PIF ATP Rankings are the merit-based method used by the Association of Tennis Professionals (ATP) for determining the qualification for entry as well as the seeding of players in all singles and doubles tournaments. The first rankings for singles were published on 23 August 1973 while the doubles players were ranked for the first time on 1 March 1976. Ranking points are awarded according to the stage of tournament reached, and the prestige of the tournament, with the four Grand Slam tournaments awarding the most points. The rankings are updated every Monday, and points are dropped 52 weeks after being awarded. Novak Djokovic is the current men's singles world No. 1.