Ronaldo left Madrid as the club's all-time top scorer after nine seasons to join Juventus in 2018 and the two have not faced each other since.
"It was special and it was a duel that will remain forever as it went on for many years and it isn't easy to keep competing at the highest level for so long," Messi told Dazn Italia when asked about his rivalry with Cristiano Ronaldo.
"More so in the two teams that we were at, so demanding as is Madrid and Barca, the best two in the world.
"Competing head to head for so many years will be remembered forever. The sporting rivalry between us was very nice on a personal level. I think that the fans also enjoyed it, be they Madrid or Barca supporters, and those who just like football in general will also have enjoyed it."
Messi won his sixth Ballon d'Or in 2019 to go one ahead of Ronaldo, who has claimed the prestigious honour on five occasions.
During Ronaldo's time in the Spanish capital he scored 450 goals in 438 matches, while Messi netted 472 goals in 476 appearances across all competitions.
The Clasico had a distinct flavour when Ronaldo was at Madrid, according to Messi.
"Obviously when Cristiano was at Madrid the games against them were always special," the Argentina captain said. "It was all the more special because of what those game mean but those times are behind us and things go on, it's what it is."