Mourinho brought Salah to Stamford Bridge from Swiss side Basel in 2014 during his second spell as the Blues manager.
The Egyptian, who was 21 at the time, only managed 19 appearances for the west London side before he was shipped out on loan to Fiorentina and then Roma – where he eventually moved to permanently.
Salah has gone on to become one of the world’s greatest players firstly building his reputation before becoming a talisman for Liverpool.
He enjoyed a record-breaking first season at Anfield, netting 44 goals as Jurgen Klopp’s side reached the Champions League final, and has already bagged 20 notches this season with the Reds comfortably in the title race.
But despite letting him go and watching him flourish, Mourinho insists Salah needed to move to Italy for a number of reasons – including to toughen up and to gain an understanding of the game.
Mourinho told beIN Sports: “He arrived at Chelsea, coming from Basel, as a lonely boy, a naive boy, completely out of context and physically fragile.
“Then he goes to Italy. He has the experience at Fiorentina, he has the experience at Roma and when he comes back to England he comes completely adapted to the high level of European football.
“He has a higher understanding of the game, he is physically much stronger you can see his body and his fitness is much stronger and much more confident.”
Salah has made his name as a winger but Klopp has been forced to move him more centrally recently due to Roberto Firmino’s injury.
But the goal machine admits he prefers it out wide.
“I have played at centre-forward a lot this season but I still also play as a winger and have scored many goals as a winger,” he told Liverpool’s official match day programme.
“I don’t like to brand myself a No.9 because the way I play, it’s never like I hold the ball and am always physically strong.