Madrid made Ronaldo the most expensive player in the world when they paid an estimated $135.2 million to Manchester United for his services in 2009.
Ronaldo scored a last-gasp winner for Madrid at Camp Nou last season to end a 39-game unbeaten run for Barca and he will once again be front and centre for Zinedine Zidane's side when it heads back to Barcelona on Sunday (AEDT).
But Laporta - Barca's president between 2003 and 2010 - has made public a conversation he held with Ronaldo's agent Jorge Mendes about bringing the then-teenager to Catalonia as he led a rebuild of the squad.
"When we [Laporta's administration] arrived, we signed Ronaldinho, [Rafael] Marquez and [Ricardo] Quaresma," Laporta is quoted by As.
"We were in a process of reconstruction. Cristiano was at Sporting CP and he was close to signing for United.
"The player's agent, who was handling Marquez and Quaresma said 'I've got another really good player who's called Cristiano Ronaldo.'
"We told him we knew about him and he offered him to us for two million [Euros] cheaper than to United, who ended up paying 19 million."