He made his long-awaited Spain debut on Sunday against Albania after finally being recognised by his country.
The Spaniard received his call-up from new coach Julen Lopetegui to the senior team for the first time since the London Olympics.
Speaking about his development, Herrera insisted he feels good under Mourinho.
“It’s been difficult to get back because this is the fifth season since the Olympics. I’m overjoyed because I have fought hard for it. I know that in the two years under [Louis] van Gaal I was not in the United team enough to be called up,” he said.
“Now with Mourinho I’m feeling good. He is putting faith in me and giving me that chance to play regularly in a top side. Now I have to show that I deserve to stay in the United XI and deserve to keep getting the call to join the Spain squad.
“Mourinho encourages me to do shoot from distances. I scored recently in the cup and I have hit the post from long-range too.
“Mourinho gives you more freedom as a player; he wants the player’s instinct to come through. It’s true that you then have to have that defensive order but he tells us to let that if that instinct guides us on the pitch then we should try things.”
Mourinho’s arrival at the club represented a new opportunity for all of the players and he has grasped the chance with both hands after a disappointing run of inconsistency under Louis van Gaal.
Herrera claims Mourinho has taken the Dutchman’s shackles off the team and allows players to shoot from distance.
It’s brilliant to hear him full of confidence and his international call-up will undoubtedly give him the inspiration to keep performing well at Old Trafford.