On Thursday he will lead Barca's midfield against the Red Devils and his former Ajax coach Erik ten Hag at Old Trafford, where he might have played this season -- safe in the knowledge his decision has been vindicated.
Ten Hag was keen on reuniting with the 25-year-old, while Barcelona's financial situation meant they would have been happy to get De Jong's wages off the books and bank a significant transfer fee.
However De Jong was at home in the Catalan capital, even though his compatriot Ronald Koeman had been replaced in Barcelona's dugout by Xavi Hernandez, less convinced by the midfielder, signed in 2019 from Ajax for 75 million euros ($80 million).
De Jong arrived at his dream club, as revealed by his partner Mikky Kiemeney on social media, where she posted a picture of the player back in 2015 at Camp Nou, visiting as a fan.
However the move turned into a nightmare as Barcelona suffered sporting, financial and institutional crises, with coaches Ernesto Valverde, Quique Setien and Koeman all sacked.
Xavi arrived and many hoped that one of the all-time greatest midfielders would be able to help De Jong improve.
However, frequently hauling him off early, Xavi seemed frustrated the midfielder could not slot into his 'positional play' gameplan.
De Jong wanted to operate as the deepest midfielder, a role which Xavi reserved for veteran Sergio Busquets, leaving the Dutchman no choice but to play higher up.
Yet despite the "95 percent" completion of his switch to United, per one Spanish report in the summer, he dug his heels in, determined to convince the Barcelona coach and establish himself where he always hoped to reach.
De Jong blamed Barcelona for leaking his contract details to the media, and was frustrated questions were raised over the validity of his deal, signed in the disastrous Josep Maria Bartomeu era as president.
"I found it really annoying that the club did this," De Jong said last November.
- 'Total player' -
Xavi's switch in 2023 to a system with four midfielders, instead of the traditional 4-3-3, has helped unlock the enigma of De Jong.
Able to play alongside Busquets at the base of the midfield instead of ahead of him, De Jong is able to see the game in front of him and influence it.
He is also able to drive forward at the right moments, without fear of leaving a gap at the base of the midfield.
No longer is De Jong expected to become the next Busquets -- instead he is seen as a complimentary player.
The Spaniard was injured in the Europa League play-off first leg, but Xavi says he is fit to return for the second.
With Pedri injured and Gavi suspended at Old Trafford, De Jong's importance to Barcelona this week is higher than ever.
"The key is the confidence we give him, how he feels, he is happy and very important in the team," said Xavi recently.
"He is a total player."
When De Jong was taken off early against Cadiz on Sunday as La Liga's leaders won to restore their eight-point advantage, he was afforded an ovation by supporters.
It was a vastly different feeling to the disappointment fans –- and the player himself -– felt last season at his performances, or the frustration writ across his face after those early withdrawals.
"I was hoping he would stay because, in the end, this is the type of player I want in my team," said goalkeeper Marc-Andre ter Stegen before the 2-2 draw with United at Camp Nou.
"I am just happy he is here. I don't want him to leave."
Nor do Barcelona now, De Jong a vital part of the puzzle when he might have been facing the Catalans instead on Thursday had they got their way.
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