United have made an underwhelming start to life under Mourinho, despite a significant outlay in the summer which saw the club pay a world record £89million transfer fee for midfielder Paul Pogba.
They currently lie six points off the Premier League's top four and speculation is rife some key members of the squad are unhappy with Mourinho's methods.
But Spaniard Herrera rejected those suggestions, saying: "We have a saying in Spain: you catch the liar before you catch the lame man
It's true in life and even more so in football
If a coach is not straight, players soon find him out
Mourinho is very straight.
"He says what he thinks and he says it to your face
He says it when it is something we will like, but he also says it when it is something we won't like.
"The team is enjoying the day to day
Training is very dynamic and everything is with the ball so the players never lose concentration - there are no really long sessions or long team talks.
"He really understands what a footballer needs which is 20 minutes of team talk and then you get down to it."
The 27-year-old may make a belated senior Spain debut against England at Wembley on Tuesday night, having worked his way into a regular starting role under Mourinho at United.
Herrera has been occupying a deeper role in United's midfield and he believes it is a step in the right direction for his career.
He added in the Daily Mail: "I have come here because Mourinho has given me the opportunity to take on a new position and I feel comfortable with it.
"I'm more defensive now, playing in front of the back four
I think I have that ability to win the ball back quickly when we lose it
I have taken a leap forward at United which has allowed me to get into the national side."
Source : PA
Source: PA