The League Cup exit means United's only realistic hope of winning a trophy this season now rests with the FA Cup.

"I'm the manager. It should be my job to understand what happened. Again, I'm really sorry for our fans. Let's focus on the next game. That is more than a result. That is the biggest problem in the team. I think it was really clear today," Amorim, whose side has picked up one point from its opening two Premier League games, told reporters.

"I would like to say very smart things and very important things. I have nothing to say. Nothing to say. That is the biggest problem also. To see the same mistakes and nothing to say in this moment. I'm really sorry for our fans.

"It's too much sometimes. You cannot change so much. You cannot change everything in one summer. You need to win games. You need to not show this kind of performance.

"I think this is a little bit the limit."

Goalkeeper Andre Onana made a dismal return to the team and was culpable for both of Grimsby's goals, as he was beaten at his near post for its opener and then failed to claim a cross that was converted by former United academy player Tyrell Warren.

"It's not about Andre," Amorim said. "With all due respect, I already said that the best team won, but this is a fourth division team. It's not the goalkeeper. It's more than that."