It was announced this week that Salah and Liverpool will part ways this summer, a year before his contract expires.
With Klopp, Salah won the Champions League and Premier League for Liverpool.
"In the moment when you work with him, it is the same as every other player: 'You can't lose the ball here, you have to defend here', all these kind of things," Klopp told The Anfield Wrap.
"But with the bigger view, it is just ridiculous. Unmatched numbers - will we be talking in 10 years and someone else has them? (Hugo) Ekitike or whoever. I think it will be really difficult (to surpass Salah).
"I think he is one of the all-time greats."
Klopp also stated: "He (Salah) was part of the best front three in world football for a long time - the one with the most numbers. That says something," the German added.
"It is not easy to be slightly above the other two guys. They all had their specific skills, but Mo was the one for the final moment. He wanted it more than anybody.
"Sadio was a mix of both - he wanted to score goals but could even play in midfield - Bobby was the genius who didn't care about anything.
"Mo was the one with a goal always in his mind. You cannot train that or learn it. It is inside him, and he has that. He will have it until the last day of his life."
He added, "We (Salah and I) texted last night. I really hope he enjoys the rest of the season. I know Mo will only enjoy it if he is winning football games and scoring," Klopp said.
"I hope on this last matchday you (Liverpool supporters) all will have a smile on your face and just be happy and thankful that you were part of one of the most incredible careers we will ever be part of."