Sanchez immediately had the weight of the world on his shoulders, with the new number seven expected to be the man to help take United back to the top - especially considering the lengths the club went to in order to secure his signature.
Of course, this proved too much. It was a nightmare time for both the club and the player, but this disastrous partnership was finally brought to an end when his contract was terminated and he completed a permanent move to Inter in August after a fairly successful loan spell.
There were too many factors at play to definitively say what the exact root of the problem was for Sanchez at United. Perhaps it was the expectation. Perhaps it was the fact he wasn't entirely keen on the idea of moving to Old Trafford until the contract offer was made. Or perhaps he didn't fit the system. Indeed, it was likely a combination of a number of factors.
But one thing that was clear was that Sanchez was visibly unhappy at the club.
Now with Inter, Sanchez recently decided to try and explain why he was unable to succeed at Old Trafford. It was an attempt from him to help fans understand the problems that arose during his time with the club which impacted his confidence and his image.
Fans have been desperate to hear his side of the story for a while, with many keen for the forward to take responsibility for his underwhelming displays. But instead, the 31-year-old took the opportunity to shift the blame and spark further anger among the United fanbase. The winger admitted he accepted the Red Devils' offer without much information, instead relying on the idea of the move sounding 'nice' to him.
As if that wasn't bad enough, he further added that after the first training session, he asked his agent if he could rip up the contract and return to Arsenal.
One training session. One!
It has become common knowledge in football that it can take footballers time to settle at a new club -take Fred at United for example. But for Sanchez, his comments simply suggest he was never set on trying to live up to the expectations, rather he was already looking for a way out and something or someone to blame after a tough first session.
Sanchez's comments, however, should act as a reminder of the work Ole Gunnar Solskjaer has done at United so far. Sure, the Norwegian hasn't won over every United fan and he is still learning, but much of the work - particularly off the pitch - he has overseen up to this point has often been largely under-appreciated.
Solskjaer has worked tirelessly since his arrival to change the dynamic within the squad and to unite the players. One quote of his perfectly highlights his efforts so far in this department: "I'd rather have a hole in the squad than an a**ehole," he said in May. "Personality is so important. We're a team in a team environment. You want players to have a bit of ego and edge but they have to be able to adapt."
Hmm, I wonder who he was thinking of....? In case you weren't sure, one name is Sanchez.
After all, this is precisely why he was so adamant to offload him on loan last summer and why he did so on a permanent basis only weeks ago. Sanchez didn't have the character, attitude, hunger, desire or willingness to succeed under Solskjaer, and the player's comments prove that the boss has been completely right to take such drastic action.
Elsewhere, Romelu Lukaku was sold last summer to Inter, with the forward going on to enjoy an outstanding first campaign in Milan. Of course, questions such as 'why did United let him leave?' and 'how silly are United to sell their best striker?' soon became rather frequent as the club came in for criticism.
But the reality is, the deal benefited all parties. Lukaku didn't want to be at United anymore, and rather than keeping him, Solskjaer opted to sell him and instead put his faith in his current young guns - all of whom have repaid his trust in them. The likes of Anthony Martial and Mason Greenwood would not have enjoyed such successful 2019/20 seasons had Lukaku still been at the club.
With regards to signings, the Red Devils have seemingly taken a major step forward and have learned from their previous mistakes. Solskjaer is insistent on bringing in players who meet a certain criteria - most importantly, players who want to play for the badge.
And no, not just the ones who will say it in their first interview after signing....like Sanchez.
The recent purchase of Donny van de Beek once again highlights this. But it is United's interest in Bayern Munich's Thiago Alcantara which perhaps best shows the progress the Premier League club have made with Solskjaer in charge.
Indeed, Solskjaer is keen on the midfielder and is said to have spoken with him directly, but his wage demands are proving to be an issue. Gone are the days of the Red Devils naively handing out mega deals in order to land a player's signature. Instead, they are now prepared to miss out on the likes of Thiago if they feel they aren't the first choice for the player.
Sanchez wasn't wrong when alluding to the atmosphere within the club and the lack of cohesion, as this was clear to see towards the end of Jose Mourinho's reign. But his desire to leave after just one training session indicates that he indeed contributed to the toxic atmosphere.
Solskjaer inherited an unhappy and disunited squad, and was faced with a major rebuilding task. And in under two years, he has already managed to implement his long-term vision, making excellent acquisitions to replace those who didn't fit into his plans along the way. The squad is now not only brimming with talent, but it's also a united group with one common goal: to succeed.
Is Solskjaer the perfect manager? No, he's not, of course not. There are still areas of his management which he must improve upon. But Sanchez's recent comments should act as a reminder of just how many positive changes Solskjaer has made both on and off the field in such a short space of time. The board must continue to back him now to provide him with the best possible chance of fulfilling his vision.