The Spanish custodian was lost for words about the Brazilian attacker and hinted that he sees the 32-year-old as a better player than Messi
The 32-year-old attacker, currently on the books of Atletico Mineiro, signed for Barca in 2003 and led the Blaugrana to two La Liga titles and one Champions League crown, winning the Fifa World Player of the Year award twice and the Ballon d'Or once in the process.
Lionel Messi has frequently been described as the best player of his generation and one of the best in the history of football, but Valdes has seemingly rated Ronaldinho higher than the Argentine.
"I have always said that 'Rony' changed the club's history when he played at Barca," he told Terra TV. "He was the leader of that team which changed [our] history.
"We had not won any title for many years. He arrived and powered Barcelona to become a club known worldwide. And that alone is a reason to thank him.
"I would say he is the biggest talent I have seen in the dressing room. He was always doing new things."
Ronaldinho, who quit Barca in 2008 to purse his career at AC Milan, signed for Atletico Mineiro last month after rescinding his contract with Flamengo following a dispute over unpaid wages.