Ronaldo was hooked on 55 minutes for the eventual matchwinner Paulo Dybala on Sunday and is said to have left the ground before the final whistle.
There is no suggestion that Ronaldo left to avoid a doping test.
"Did he leave before the end of the game?" Cassano asked on Tiki-Taka.
"You can't do that because there is an anti-doping control,' he explained.
"I had to go back to the stadium urgently to avoid a two-year ban."