The midfielder, who has fallen out of favour at Parc des Princes amid uncertainty over his future, was not part of the matchday squad and hasn't played for Thomas Tuchel's side now since December 11.
Indeed, the player's situation has been the subject of much controversy in 2018-19, with Rabiot having even been barred from training with the first team after refusing to discuss a contract extension with the club.
That led to the National Professional Footballers' Union (UNFP) of France calling on PSG to end their exclusion of the player, claiming the treatment of the France international is illegal and borders on "harassment".
Barcelona have been strongly linked with signing Rabiot on a free transfer when his contract comes to an end in the summer of 2019.
Confirming that Rabiot would be leaving PSG, the player's mother and agent Veronique Rabiot revealed that Barca had made an offer in the 2018 summer transfer window that was blocked by the Ligue 1 leaders.
And the PSG fanbase will not have been impressed after images and clips of the 23-year-old surfaced on social media showing him in a nightclub enjoying himself on what was a painful evening for Tuchel and his side.
La défaite du PSG d'hier soir ?? Rabiot n'en a rien à foutre. Il est partie en boîte juste après le match sombre merde va (vidéo sur instagram (isaachaddad) pic.twitter.com/wCrtVY17Fm— BADDIE👩🏻💻 (@baddieparisian1) March 7, 2019
The Ligue 1 champions went into the second leg against United confident of securing their progression to the quarter-final of the Champions League, with the French side holding a 2-0 lead from the first meeting between the two.
Two goals from Romelu Lukaku, either side of a Juan Bernat equaliser, gave United genuine hope of completing a miraculous comeback, however, before Marcus Rashford's stoppage-time penalty finished the job.
The despair on the faces of the PSG players at the full-time whistle was clear to see, although the result did not appear to have affected Rabiot.
"I find unacceptable the attitude and lack of professionalism of a player like Adrien Rabiot towards the club, his teammates and his supporters,' PSG sporting director Antero Henrique told RMC Sports on Thursday.
And it is not the first time that he's courted controversy over his actions, with the midfielder having famously declined the chance to be on his national team's standby list for the 2018 World Cup - a tournament the French would, of course, go on to win.
PSG will now turn their attentions back to league matters ahead of their meeting with Dijon on Tuesday, with the Parisians a massive 17 points clear at the top of the Ligue 1 table.