The Real Madrid attacker does not believe that football has a problem with drugs, and insisted that he has not fallen out with coach with Jose Mourinho
Former Real Sociedad president Inaki Badiola claimed earlier this week that the Basque side bought banned substances during a six-year period between 2001 and 2007.
However, the club have since moved to deny the allegations, and Ronaldo, too, feels that there is no room for doping in the sport.
"It's a very delicate situation, but I don't think there is doping in football," Cristiano Ronaldo was quoted as saying by AS.
"It's a collective sport and I don't think it's necessary to resort to doping to improve your performances. But I can't swear that no-one has done it.
"Is football a clean sport? Yes, 100 per cent. I don't think these types of things exist."
The attacker had a heated discussion with head coach Jose Mourinho after the match against Valencia earlier this season, but Ronaldo has insisted that his relationship with his boss is fine.
"These kinds of things are personal. Everything's been settled and is fine again. What happens in the dressing-room should stay in the dressing-room."