Debate rages over who the world's best player is, but a shortlist of two is almost universally accepted – it is either Messi or Ronaldo.
The Portugal forward has since departed for Juventus, but Messi – who won a record sixth Ballon d'Or in December – has fond memories of their long-running Spanish saga.
"The matches against Real always mean a lot, but when Cristiano was there they became much more special," said Messi.
"But it's a time that has passed now, that we have experienced. Now, we have to look ahead to the future.
"It was a special duel and it will remain [in people's minds] forever, because it lasted for many years and it is not easy to maintain such levels for a long time.
"Plus, the teams we played in were also very demanding, both Real Madrid and Barca, the two best teams in the world.
"The sporting duel between us was very nice on a personal level and I think people had fun too, whether they were fans of Madrid or Barca, or even only football fans in general."
Barca this week appointed a new head coach, with Quique Setien replacing Ernesto Valverde, despite the club sitting joint-top of the table with Madrid.
The last Clasico clash ended 0-0 at Camp Nou in December, with Barca set to head to the Santiago Bernabeu in March.