The 19-year-old, who has made 40 appearances so far this season, has attracted criticism from some sectors for failing to manage a Premier League goal since September.
It was recently reported, however, that Rashford had been spending extra time on his shooting at Carrington, often staying behind after training to practice on his own.
And Mourinho, speaking after the 1-1 draw with Everton, was quick to leap to the youngster’s defence.
“We have people that are not getting [taking] the opportunities and that’s bad for the team,” he said. “But I speak with them because when you give absolutely everything and you leave the pitch absolutely dead of work, that’s fine for me.
“Marcus Rashford doesn’t score goals since September [in the Premier League] – the only thing he deserves is support. Nothing else. Support, no critics, support. He works, he works, he works. He tries, he plays through the middle, he goes to the left, he goes to the right, he tries, he tries, he tries.
“The kid is desperate. It’s not a surprise for me – the second year not being as good as the first one. Maybe one day I will try to find out if it happened with Ryan Giggs or someone. They appear as a kid and then the next year it’s not the same. But the kid is phenomenal – an amazing professional. So no problem. I told him – keep going.”
If last season was an affirmation of Rashford’s natural brilliance, this season serves as an affirmation of his desire to commit everything to the cause, regardless of circumstances.
The game against Everton was a potent example: the game started poorly for the youngster, seemingly unable to get a firm hold on the ball, but he kept at it, refusing to shirk away, and eventually started to impose himself on the game with a series of powerful runs.
Most teenagers would retreat into their shells following a bad start to a game; Rashford, on the other hand, felt compelled to work even harder – a true hallmark of a genuine professional.