It will be a battle of the veteran goalkeepers when Porto welcome Italian champions Juventus to Estadio do Dragao for the first leg of their last-16 tie on Wednesday.
And Casillas - who is in fine form himself as he tries to earn a Spain recall - heaped praise on Buffon.
"I am lucky enough to be three years younger than Gigi. I was 14 when I started and he was 18; I was able to see and appreciate his style and personality," the 35-year-old former Real Madrid keeper told UEFA.com .
"As I grew up, I looked up to him and then we evolved together and we've had similar careers. We've both won a lot and we've often played against each other.
"I think Italian football won't have another goalkeeper like him.
"In Europe and around the world, he's considered one of the best of all time. Ours is a healthy, positive rivalry: we really appreciate each other and playing against him is always a pleasure.
"He is a player who is known and admired all over the world and he is part of the history of this game."