VIDEO: Ruben Amorim launches furious attack on Man Utd players after embarrassing Carabao Cup exit as Red Devils boss vows to fix mounting problems

Charles Vernam lit up the night with a superb 22nd-minute strike that arrowed beyond Andre Onana. United’s defence, already fragile this season, was exposed again just before the interval as Onana failed to deal with a routine delivery and Tyrell Warren pounced to poke in Grimsby’s second. While Bryan Mbeumo and Harry Maguire scored in the final quarter to take the game to penalties, the former struck the woodwork in his second attempt to hand Grimsby their place in the next round. 

After the match, Amorim lashed out at his players and said: "I know that the best team won. The only team that was on the pitch. The best players lost. Any team can win against group of players. I think that the team and the players spoke really loud today. That’s it. We lost, the best team won. It’s not just the space [Manchester United gave Grimsby], but the way we started the game without any intensity. All of the ideas about the pressure, we were completely lost. It is hard to explain."

The defeat piles even more pressure on Amorim, who is still chasing his first Premier League victory this season after losing out to Arsenal and drawing against Fulham in the first two top-flight matches. United’s start to the campaign has been chaotic, their defensive weaknesses glaring, and their attack worryingly toothless. To be outfought and outplayed by a League Two side has left supporters furious, questioning both the commitment of the players and the direction of the club under the Portuguese.

There is no respite for United as they must turn their attention back to the league, with Burnley visiting Old Trafford on Saturday. Already, the fixture has the feeling of a must-win game, not just to secure points, but to calm a fanbase that is rapidly losing patience.