This has been a galling campaign for United with injuries crippling Erik ten Hag's options, ample issues off the pitch with discipline, a harrowing Champions League campaign where they finished bottom of the group, and they are way off the pace in the Premier League.
But for the first time in a while United looked much the superior team, looked like a side that, with injuries clearing up, could now begin to go through the gears for a strong end to the campaign.
And so imagine the hush that descended on Old Trafford when, after a tussle on the byline with Vladimir Coufal, Lisandro Martinez went down, teeth gritted and immediately clutched his right knee with both hands.
If ever anyone was to question the Argentine's importance to this team it was laid plain when five team-mates - including Casemiro, Andre Onana and Luke Shaw - rushed to his aid. Martinez knew immediately something was seriously wrong - and so did his team-mates. Disaster had struck.
Lisandro Martinez is facing eight weeks sidelined with medial collateral ligament damage
The Argentine defender injured himself after tangling with Vladimir Coufal during the match
Concerned team-mates surrounded Martinez after the collision with the Hammers defender
Fears of a season-ending ACL injury were, at least, allayed on Monday - good news - when United confirmed it is medial collateral ligament damage, likely sidelining him for eight weeks,
No trip to Aston Villa; no FA Cup fifth round; no Manchester derby; arguably United's most important player is going to have to watch them all from the sidelines - again.
'He is very sad, very disappointed. We all feel really with him,' a deflated Ten Hag said on Sunday.
'First of all, it is a personal disaster when it is really bad, but also for the team it is really bad because he definitely brings us a lot.'
Martinez looked out of sorts at the beginning of the season, evidently still feeling the effects of the surgery he had had on a broken metatarsal back in April that prematurely ended his 2022-23 season.
A second surgery on it kept him out for three months of this campaign and United's defensive fragility proved no surprise in Martinez's absence.
He is the best defender Erik ten Hag has and his absence this season has been keenly felt
The Argentine star looked visibly disappointed after having to leave the field with the injury
West Ham was only his 10th appearance of the season, and only his seventh start. Without him, United cannot do what they want to do in terms of building from the back.
GAMES LISANDRO MARTINEZ IS SET TO MISS WITH INJURY
February 11: Aston Villa (A)
February 18: Luton Town (A)
February 24: Fulham (H)
February 28: FA Cup fifth round (A)
March 3: Man City (A)
March 9: Everton (H)
March 16: Sheffield United (H)
March 30: Brentford (A)
April 3: Chelsea (A)
There was one moment away against Newport County in the FA Cup where Martinez picked his head up, shifted the ball from his foot and clipped a delightful cross-field ball to Alejandro Garnacho, who went on to crash his strike against the crossbar. No other defender in United's ranks could have pulled that off.
And that's the root of the problem. No other defender can provide what Martinez can in terms of ball-playing ability, as well as that aggression that sets the tone in a match.
Since his return, which had been carefully managed by Ten Hag, United have won three and drawn one. That's no coincidence.
Widen the stats out and of the 47 matches Martinez has played since his £47million move from Ajax, United have won 32, drawn four and lost 12. That's a win rate of 68 per cent.
Contrast that to a Martinez-less side and in the 48 games he has not started, United have won just 25, drawing eight and losing 14. That's just 52 per cent of wins without him. It's night and day.
'You look at the personnel – I think having Martinez coming back is great, because he looks like a real winner and a leader in the dressing room,' former Arsenal striker Alan Smith told BritishGambler.co.uk.
'The signing of players personality-wise was something that Sir Alex looked at in depth, in terms of their character, not just their ability. Ability can be measured in many different ways.
'To play for Man United, the scrutiny is still there, regardless of them not winning the Premier League for however many years. It's still probably the biggest scrutiny in football. Manchester United, Real Madrid and Barcelona – they're probably the three that get scrutinised the most. It takes a certain type of person to embrace that.'
A fan favourite, his blend of ball-playing ability and pure aggression is unmatched in squad
His return had been carefully managed but he now faces another long spell on the sidelines
Ten Hag has made no secret of how much of a difference it makes to his football when he has Luke Shaw and Martinez available as his first choice left back-left centre back pairing. Now he is going to be forced into another reshuffle ahead of a huge game in the race for the Champions League away to Aston Villa.
One option is to push Shaw inside, use someone like Diogo Dalot at left back and Aaron Wan-Bissaka, who missed the West Ham game, at right back.
Another is to keep Dalot and Shaw in their regular positions and partner Harry Maguire, who deserves an immense amount of credit for how he has improved his stock at United this season, with Raphael Varane.
The downside to that is that Ten Hag just doesn't like it, he's made no secret of that.
'There are moments in certain games where they [Maguire and Varane] can play together and they have already proven they can do it. But the buildup is not that fluid when one of them is playing from the left centre back position because I think Licha [Lisandro Martínez], obviously, Luke Shaw, obviously, Jonny Evans and Victor Lindelof, they are right-footed, but they can play really comfortably with their left and make the right angles, then you can construct a better formation where you can start to play,' he said earlier this season.
Jonny Evans, who stepped in and performed admirably at the start of the campaign, is Mr Reliable, albeit no Martinez, while Victor Lindelof is another option.
Raphael Varane (right) replaced him against West Ham but Ten Hag is not fond of partnering the Frenchman with Harry Maguire, who looks second in the rankings only behind Martinez
It's been one of those seasons for Martinez, with injuries striking just when he builds up form
The issue is that everything is a step down from the levels that Martinez can provide.
Aside from a brilliant assist away at Burnley for Bruno Fernandes to volley in, Evans hasn't got the passing repertoire of 'The Butcher'. Lindelof provides even less in that department.
Rio Ferdinand summed up Martinez last year when he said: 'He's dominant, he's aggressive, he's a leader, he communicates well, he shows character and he is there in big moments.'
And just when United looked to have that successful blend back in the side, disaster struck. It's been that kind of season for Martinez and for United.
For Ten Hag, it's back to the drawing board.
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