Manchester United are reeling from a Carabao Cup calamity at Grimsby that has invited scrutiny and fresh questions over the future of head coach Ruben Amorim.

Despite seeing a deserved victory snatched away when Harry Maguire’s last-gasp header snatched a 2-2 draw, the League Two side were not to be denied as they beat the wretched Red Devils 12-11 on penalties.

The ignominious exit leaves scars and highlights issues around the stumbling Old Trafford outfit and their under-fire manager just three games into the new season.

What has the mood been like at United?

New signings, a revamped training ground and promising pre-season had seen optimism return to United just three months on from the damaging Europa League final loss to Tottenham compounding their worst top-flight campaign in 51 years.

But things have quickly turned, with a promising performance in the 1-0 home loss to Arsenal followed by Sunday’s bumpy 1-1 draw at Fulham and, most alarmingly, the deserved loss to a League Two opposition.

United somehow managed to put in an even more disturbing display against Grimsby than Louis van Gaal’s side did in the 4-0 loss at League One outfit MK Dons at this stage of the competition in 2014. Wednesday night felt like the nadir of the post-Sir Alex Ferguson era.

What went wrong against Grimsby?

Every aspect of United’s display disappointed Amorim, whose side were outthought, outfought and overran in an abysmal first half. Andre Onana, making his first appearance of the season, should have done better for the first goal and gifted the hosts a second, but it was about more than just a blundering goalkeeper.

United, who made eight changes, reverted to the soft, stumbling side that failed last season. Three players were replaced at the break, yet it could easily have been more and Diogo Dalot admitted the players lost an opportunity to show they deserve to be at the club.

United were incoherent out of possession and toothless in it, with their performance lacking the courage and spirit shown by Grimsby. Just as worryingly, Amorim at times looked as overawed as his players. The image of him sat in the dugout during the shoot-out will live long in the memory.

What is the situation with Amorim’s position?

“You’re getting sacked in the morning” echoed around Blundell Park during and after Wednesday’s exit. However, there were no noises from the club the following day that Amorim’s future was in imminent danger – unsurprising, considering previous backing and the early stage of the campaign.

Still, bookmakers slashed odds on his departure and he himself raised questions over his future. Amorim had considered his position just months after succeeding Erik ten Hag last November and then offered to leave if the club wanted him to after May’s final defeat to Spurs.

Few expected to hear similar utterings in August but the exasperated coach said “players spoke really loud today what they want” and that “something has to change”.

How much more rebuilding can be done?

Monday marks the end of the transfer window and there remains a lot to do. United are attempting to sign Antwerp’s Senne Lammens to bolster their shaky goalkeeping department and midfield remains an issue. They had cooled their pursuit of Carlos Baleba due to Brighton’s determination to keep him.

United are yet to shift four of their five-man ‘bomb squad’ or so much as sell a player for a fee. While Marcus Rashford has joined Barcelona on loan, negotiations have dragged on over the potential departures of Alejandro Garnacho and Antony as the futures of Jadon Sancho and Tyrell Malacia remain up in the air. Rasmus Hojlund looks set to leave and Kobbie Mainoo has been linked with an exit as United head for a hectic end to the window.

What is next for United?

Nothing but victory will do against promoted Burnley on Saturday afternoon otherwise United will head into the first international break of the season in the eye of a storm.

Amorim plans to take stock during that period, with a trip to rivals Manchester City, home game against Chelsea and trip to the unhappy hunting ground of Brentford coming up in September.