Herrera expressed his disappointment at losing Saturday's derby.
Herrera told MUTV: "We lost the derby against our local opponents and tomorrow our fans are going to face friends who are City fans. I feel sorry for them.
"We are trying to win every game but it cannot happen. We knew it [not winning] was going to happen sooner or later. Ideally it could have happened later but this is football and we are going to get stronger."
Reflecting further on the game, United's number 21 added: "City won the game in the first half. We cannot make excuses now. We just have to think about the next game and try to win at Feyenoord.
"We must look forward, be balanced in our minds and not go crazy - it's only the fourth game of the season. But of course when you lose a derby against your local opponent it's painful."