The Egyptian winger joined the Blues from Swiss club FC Basel for £11million last month and has thus far made two substitute appearances in the Premier League and one in the FA Cup in the 2-0 loss to Manchester City on the weekend.
Of that second-half performance, Mourinho felt Salah was not quite at the level required but feels he will adjust over the next few months in order to become a top player at Stamford Bridge.
"He was not in the game (against Manchester City). He has that (pace) but he was not in the game," said Mourinho.
"It's important for him to come step by step and try to improve and adapt. This is a different world, a different quality of football to the one he comes from.
"You know, playing at Stamford Bridge is not the same as playing for Basel.
"With Basel you play to enjoy your time and you have nothing to lose. While in the blue shirt, you have 40,000 people that you are required to please. Everyone wants you to be decisive, all the time.
"So I think Mohamed needs six months to adapt to our game and the demands of the Premier League.
"I am calm and I'm telling him he has time because we have confidence in him. I think next season is Mohamed Salah's breakthrough season."
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