The Potuguese worked with the Egyptian at Chelsea but his stock has risen considerably since moving to Liverpool, who face United at Anfield today.
Mohamed Salah carries a “nuclear” threat to Manchester United when they face Liverpool, according to Jose Mourinho.
Salah played under Mourinho at Chelsea, but his initial spell in the Premier League failed to catch fire and the former Basel man moved to Serie A.
He returned last season, joining Liverpool for £36.9million following spells with Fiorentina and Roma, and Mourinho acknowledged the Egyptian forward has made considerable strides since they worked together.
“He has developed incredibly well at every level,” he told reporters of a player who is a key factor in there being a 16-point chasm between title-chasing Liverpool and their bitter rivals United.
“Physically, an amazing development. He was a fast, fragile boy and now he is a fast, strong man.
“He was psychologically not adapted, coming directly from a small club in Switzerland [Basel] to a big club in the Premier League.
“It was too much. I remember I played him at White Hart Lane and at the Etihad and it was too much for him.
“Now he plays everywhere against any team – he can go to Barcelona, can go to Madrid and he plays like, ‘I am Mo-Mo Salah and I am afraid of no one and nobody’.
“He is a fantastic player, completely different from the potential player we bought from Basel to Chelsea. He was a projective player and now he is one of the best players in the world.
“I think the fact that I know him does not help me because I knew the projective player and now he is a top player.”