Ronaldo quit Real for Juve last week.
“It is an unforgivable error that Real Madrid will pay a heavy price for," Calderon told La Gazzetta dello Sport.
“People talk of Kylian Mbappé or Neymar, but they are a long way off Cristiano's level. It was an historic purchase nine years ago and the €1bn clause showed he was not for sale.
“(Florentino) Perez will pay for this error. Cristiano is the Number 1, so the damage done is enormous. Cristiano turned down the improved contract given to him by Perez lately. The reasons for walking are emotional, buy it's a great deal for Juve.
“I can see him with other trophies in the cabinet this time next years and will have to give the Champions League serious consideration.
“The cost of the operation is expensive, but will be wiped out by sponsors and advertising money. I'd put Ronaldo on the same level as Alfredo Di Stefano, Pepe and Johann Cruyff."