Salah and Ronaldo will face off in the Champions League final in Kiev on Saturday.
And while Salah has pipped Ronaldo by two goals with his tally 44 this season, Karius believes he needs to repeat his efforts year after year to belong alongside the Portuguese superstar.
"This season is unbelievable. He's of course in that region but the biggest difference is Ronaldo did this over so many years. It's too early to put Mo with him", Karius told Sky Germany.
"I don't want to take anything away from Mo - he's world class this season. But Ronaldo showed over so many years to be up there with the best, you have to prove it season over season.
"I hope he can do it. I wish he can do it. He's still really young and has a lot of space to improve even more."