Ronaldo - dubbed 'El Fenomeno' during his glittering playing career - won 13 titles at club level as well as two World Cups with Brazil in 1994 and 2002.
Ibrahimovic has faced the likes of namesake Cristiano Ronaldo during his own stellar career to date, but he insists the World Cup's record goalscorer remains the greatest he ever played against.
"The best opponent of my career? I've played against many, many good players, so I don't know who to keep. But I would say Ronaldo, 'El Fenomeno'. Why? Because he was my idol and because, as a football player, he was complete," he told Sports Illustrated.
"There will never, in my view, be a better player than him."
Ronaldo, who scored more than 350 goals in just over 500 club games during a career badly affected by injury problems, retired from football in 2011.