And so, the eagerly anticipated reunion with Ruben Amorim ended in defeat for Manchester United, with Michael Carrick's side suffering a second-half collapse to lose 4-2 against AC Milan.

It had all started so brightly following Harry Maguire's early header, albeit with a mix-up involving the Englishman and Andrey Santos seeing the Serie A side equalise before the break.

Another defensive error, this time by Amorim's side, allowed Patrick Dorgu to capitalise to make it 2-1, yet a flurry of changes culminated in United shipping three unanswered goals away in Poland.

Not the best way to sign off, ahead of the start of the new Premier League campaign, and while it is only pre-season, there's still plenty for Carrick and co to ponder.

Worrying signs for United as Ruben exacts revenge

When that man Maguire powered home inside two minutes, it looked like Amorim was on course for a grim afternoon in the Polish sunshine, just six months on from talking his way out of a job at Old Trafford.

Instead, the 40-year-old had the last laugh to secure his first win as Milan boss, while for United, a first defeat of the summer will have questions being asked of INEOS' recruitment drive.

There were, of course, some understandably sluggish showings from those returning from the World Cup, with the likes of Kobbie Mainoo and Lisandro Martinez looking a little heavy-legged off the bench, the Argentine seemingly running through treacle when trying to chase down Ruben Loftus-Cheek for the game's final goal.

Those signs of rust can be excused, as they perhaps can for the typically reliable, Bruno Fernandes, the Portuguese playmaker notching yet another assist, albeit while missing a second penalty in a week amid a largely muted showing in midfield.

More worryingly might well be the performance of the backline, with Senne Lammens bailing out those ahead of him on a handful of occasions, the Belgian making five saves in total.

Indeed, the aforementioned Maguire looked off the pace despite netting the opener, enduring that moment to forget for Samuel Chukwueze's equaliser, while also allowing Goncalo Ramos to enjoy a free header inside the area to make it 3-2.

The performance of the 33-year-old summed up the afternoon for Carrick's experienced core, in truth, with other senior members of the starting lineup also looking well below par.

Why Man Utd need to spend after dismal 3/10 performance

This result and performance could well have been washed away had it been a team littered with promising young talent and teenagers, but Shea Lacey aside, there were no current academy players who featured against Amorim's men.

That makes the 4-2 result even harder to swallow, and with time running out both before the start of the season and before the end of the transfer window, INEOS need to act.

One key area of concern remains at left-back, and if signing the likes of Lewis Hall wasn't a priority already before this week, it must surely be now.

On Wednesday night against Leeds United, for instance, young Harry Amass simply couldn't live with the lively Wilfried Gnonto after the break, while it was Luke Shaw's turn to look all at sea this time around.

Heading into his 13th season as a Manchester United player, Shaw looked more like a fresh arrival out of the academy than a seasoned pro, having found himself in no man's land far too often.

For Milan's first of the day, for instance, Chukwueze was on his own at the back post, while the former Fulham loanee also had acres of space down United's left flank to pick out Alphadjo Cisse to make it 2-2.

It was Chukwueze again who Shaw allowed to come inside to tee up Ramos less than ten minutes later, with those woes compounded soon after as a simple one-two saw Loftus-Cheek to get round both the long-serving left-back and the retreating Martinez.

​​​​​​Shaw did show flashes at the other end, delivering three key passes including a deft dink to find Fernandes late on, but it was a chastening, ambling display otherwise.

In all, the 31-year-old was dribbled past twice, won none of his ground duels and didn't complete a single tackle, losing the ball seven times from his 44 touches.

Perhaps the decision not to replace him at any stage with young Amass was a nod from Carrick to the board that he needs investment in that department, with that 3/10 performance from Shaw having not been up to scratch.

Yes, he creditably shook off his fitness woes to start all 38 Premier League games last term, but that run of one game a week exists no longer.

Equally too, the former Southampton man may have been an everpresent, but there was often a reserved or contained nature to his performances last term, rarely seen bombing forward as he picked up just one goal and one assist, while damningly creating only a solitary 'big chance'.

At least £60m might be required to sign the aforementioned Hall by all accounts, yet on the evidence of this week, not signing a new left-back could prove detrimental to Carrick's hopes this season.