That is how he has to adapt his mindset to be a key player for manager Ruben Amorim.
Rashford and Garnacho were left out of the squad for the 2-1 win over Manchester City in the Premier League on Sunday.
Post-game, defender Diogo Dalot stated: "If you want to succeed at this club, you have to suffer.
"If you’re ready to do that with us, we are going to be a good team. If not, there is no space for you."
He added: "The message was clear from the beginning - if you want to succeed if you want to thrive, you have to suffer.
"That’s not just in football but in life. If you want success, you have to work hard and suffer."
Dalot said: "The reality is this is step by step.
"With the new manager, we are progressing, taking very good steps to where we want to go — but it will take time.
"The last couple of years we had some crazy games like this, fighting until the end, and that’s the DNA of this club.
"We showed character and, even when we were losing games, our emotions were kept in control - which is progress from the last couple of years.
"When we were trailing against City we could have lost our heads."