The 24-year-old - who was loaned to Chelsea in a deadline-day deal that should be made permanent in 2025 - spent the second half of last term with erstwhile team Dortmund after his high-profile falling-out with Erik ten Hag.
Sancho and Ten Hag were at odds for months after the Dutchman left the winger out of the matchday squad for their 3-1 loss to Arsenal in September 2023, claiming that his poor performances in training were to blame.
The Manchester City academy graduate rejected his manager's version of events, effectively calling him a liar with a bombshell social media statement and subsequently being ostracised from the group.
Sancho was not allowed near the first-team facilities, and all the signs pointed towards a permanent parting of the ways in January, but the Red Devils were not able to find any buyers for the winger.
Man United 'asked pundits to stop praising Sancho'
Dortmund allowed Sancho to return to the Signal Iduna Park on loan, though, and he found safe haven with the Black and Yellows, playing a key part in their run to the Champions League final.
Sancho earned high praise while donning the yellow strip, scoring three goals and setting up three more in 21 appearances while also starting every match in the Champions League knockout stages.
As the Englishman's performances were lauded by fans and the media alike, ESPN claims that Man United actually asked pundits not to wax lyrical about him, as it reflected badly on their club.
Sancho's Dortmund zenith came in the first leg of their Champions League semi-final against Paris Saint-Germain, where he completed an astonishing 12 dribbles in one game as the German side prevailed 1-0.
No English player in the history of the competition registered more in one match, and his 12 dribbles was also the highest figure of any player in a Champions League contest since Lionel Messi in 2008.
What did the pundits say about Sancho?
Sancho's performance that evening was given a glowing review by Ally McCoist, who aimed a sly dig at Man United by claiming that the attacker's renaissance was due to him being at a club where he was "liked".
"Sancho looks like a different player entirely. His body language is like the player Man Utd bought," the former Scotland striker told TNT Sports on the night.
"You can tell a lot from body language and he wants to take people on and play. He certainly looks rejuvenated. It is confidence, he has his mojo back. He is in an environment where he is liked and he looks like a different footballer."
Sancho and Ten Hag eventually buried the hatchet, and the latter allowed the attacker to return in pre-season, but he was not re-integrated into the competitive squad before the Dutchman was sacked from his position.
Man United and Chelsea will be locking horns in Sunday's Premier League blockbuster at Old Trafford, but Sancho - who has been suffering from a recent illness - cannot play against his parent club, currently under Ruud van Nistelrooy's wing before Ruben Amorim is sworn in later this month.