In the end, Man United lost despite trying to equalize the score to 2-2, but they were unlucky in the long penalty shootout. 
Some people questioned what happened to the Man United team causing them to lose to the underdog team.
It is possible that with this defeat more fans will be fed up with the result even though it is a small tournament, the defeat of a big team still causes ridicule.
I don't know what happened to the Man UTD team but all I could say from a spectator's perspective is that the Red Devils got too confident in themselves thinking that they would be the first to open the goal scoring but alas it was like a dream to them when Grimsby scored first and not long after opted for the second goal which was ruled out for offside.Some people questioned what happened to the Man United team causing them to lose to the underdog team.
It is possible that with this defeat more fans will be fed up with the result even though it is a small tournament, the defeat of a big team still causes ridicule.
In competitions like this, no matter how small the team is, you have to play it like it's the finals because aside from the fact that these smaller sides would be happy that they qualifed, it would also be a thing of pride to note that they were able to beat a big club in the EPL and not a club in the same ranks as them.
It seems there's no way to solve Manchester United's problems with Amorim as manager.
Remember when Manchester United said they didn't need a new goalkeeper and still trusted their current one? The proof is that Onana made another fatal error during Grimsby's second goal in the EFL Cup victory.
Amorim isn't a reliable player, even though management has made it easy for him to transfer and other things.
Amorim should see how Kobbie Mainoo plays his role in midfield.
Manchester United's situation will continue to be uncertain, including in their next match against Burnley at Old Trafford.