When Argentina plays Algeria on Tuesday and Portugal takes on Congo on Wednesday, two of soccer’s most storied players will begin what will likely be their last runs at the World Cup.

Argentina star Lionel Messi, 38, and Portugal’s Cristiano Ronaldo, 41, defined soccer for much of the 21st century. Both are now in the twilight of their careers, and while there are certainly no guarantees, if both countries advance to the knockout stage, there could be one last match between the all-time greats.

From 2008 to 2017, Messi and Ronaldo were the only two players to win the prestigious Ballon d’Or, widely considered the top individual prize in the sport. Over that period, each player won the award five times, with Messi winning the award three more times since.

At the height of their careers, Messi and Ronaldo were not only battling for international supremacy, but also routinely faced each other at the club level. The two stars poured gasoline on the fiery rivalry between Barcelona and Real Madrid in La Liga, with Messi starring for Barça from 2004 to 2021, while Ronaldo played for Los Blancos from 2009 to 2018.

In 37 head-to-head matches (which includes a club friendly in 2023), the two players have been relatively equal individually, with both scoring 23 goals. Messi holds the advantage in wins, however, with a record of 17-11-9 in his career against Ronaldo.

While the two were seemingly in an eternal battle for best player alive and perhaps best player ever, Messi earned a little separation from Ronaldo since the peak of their rivalry. He leads in total Ballon d’Or awards, eight to five, and he led Argentina to a World Cup victory in 2022. (Portugal’s best World Cup finish with Ronaldo is fourth place.)

The rivalry has also cooled considerably over the last eight years or so, particularly after Ronaldo left Real Madrid for Juventus in 2018. Since 2020, Messi and Ronaldo have only played each other twice: A Champions League match in December 2020 and a club friendly in 2023.

Neither player is even competing in Europe anymore, as Messi has played for MLS’s Inter Miami since 2023 while Ronaldo left for the Saudi Pro League’s Al-Nassr the same year.

The lack of battles between the two greats has added extra juice to this World Cup, as it could be the last time the two legends ever face off if they can get their teams to the knockout stage.

In addition to the rivalry, Ronaldo is also looking for his first World Cup title in what he has said will be his final appearance at the tournament. Though it’s the biggest trophy missing from his shelf, Ronaldo last year said that winning (or losing) the World Cup won’t define him as a player.

“If you ask me, ‘Cristiano, is it a dream to win the World Cup?’ No, it’s not a dream,” Ronaldo said last November. “Define what? To define if I’m one of the best in history, to win one competition, [of] six games, seven games. You think it’s fair?”