The Brazilian joined Barca in 2004 and set about becoming the world's best player just as Messi was making his debut.
The Argentine has since gone on to win the Ballon d'Or four times himself and is grateful for Ronaldinho's help in those early years.
"I've always said, since the first moment I walked in the locker room, Ronaldinho and the other Brazilians, Deco, Sylvihno and [Thiago] Motta welcomed me," Messi told Barca TV. "But mostly [Ronaldinho], I learned a lot at his side.
"It was a big help. It's never easy going into the locker room as a teenager and Ronaldinho made everything easier. I was fortunate to live near him and share many things with him. I can say that he is a great person.
"Ronaldinho was responsible for changing the club. During the first year we did not win anything but people loved him. Later came the titles. I believe Barca should be forever grateful for everything he did."
The Brazilian star moved on to AC Milan in 2008 and is currently playing back in his homeland with Atletico Mineiro.