The Brazilian icon was at the peak of his powers at Camp Nou when a fresh-faced teenager emerged from the famed La Masia academy system.
The two South American stars complemented each other for a brief period, but Ronaldinho moved on to AC Milan in 2008.
Two-time World Player of the Year Ronaldinho has seen his former colleague in Catalunya go on to collect five Ballons d’Or and countless other records and awards, and he believes Messi tops Ronaldo as the best in the world.
Asked again during a promotional trip to Malaysia to pick between Messi and Ronaldo, Ronaldinho said: "Messi. I would have loved to continue playing alongside him.
"I didn't get enough time with him, he was very young. I'd love to take to the pitch with him one more time."
Messi is leading a treble charge at Barcelona this season, with Ronaldinho hoping to see the Liga leaders and Copa del Rey finalists get their hands on the Champions League crown.
He is, however, also looking for another of his former clubs to conquer the continent at some stage, with Paris Saint-Germain having spent big in an effort to topple the European elite.
"In football, even when you sign great players you need some time to put together a winning team," Ronaldinho added on PSG, who broke the world transfer record to sign Brazil international Neymar for €222 million in the summer of 2017.
"I believe in the next few years they will win the Champions League."
Ronaldinho won that trophy just once during his distinguished career, back in 2005-06.
He was, however, to also taste La Liga, Serie A, Copa America and World Cup triumphs and claims to have no regrets from his playing days.
He said: "I don't really have any regrets.
"I ended my playing career having fully realised all the dreams I had; individually and with the teams I played for. I'm a satisfied man."
(goal.com)