After a disappointing campaign in terms of style and substance at Old Trafford, the door is now open for Mourinho's return to management. However, the future of Ryan Giggs remains uncertain.
Before the celebrations had even subsided at Wembley on the weekend, United's FA Cup win was being overshadowed by fresh reports that Van Gaal was to be replaced by the former Chelsea boss in the coming days.
United have steadfastly refused to comment on speculation regarding their managerial situation, while the Portuguese kept his counsel when asked about the job by Press Association Sport on Saturday evening.
But with an announcement widely expected, some media outlets began to report that Van Gaal had already been shown the door - with a $10 million severance package in hand.
Van Gaal stood firm when asked about his position in the post-match press conference at Wembley, but fuelled speculation on Sunday by telling a reporter outside the team hotel that "it's over".
The brevity of the comment meant it was not immediately clear whether that meant the former Netherlands manager had been told his time at United was at an end, although his situation could soon become clearer.
Van Gaal arrived at United's Aon Training Complex at around 8.45am local time on Monday, his Mercedes sweeping into the Carrington training ground.
Two years ago predecessor David Moyes attended a morning meeting with executive vice-chairman Ed Woodward at the club's training complex and a statement confirming the Scot's sacking followed shortly afterwards, just 10 months into a six-year deal to replace Sir Alex Ferguson.
Van Gaal was followed into United's training ground by employment lawyer Paul Gilroy QC, who has long worked with the League Managers Association.
Having initially been turned away by security, he was allowed into the complex around an hour after the Dutchman arrived.
Gilroy lists former United manager Moyes among the clients he has advised, along with Ferguson, Roy Hodgson and Brendan Rodgers.
Chambers and Partners describe Gilroy as "a noted employment specialist" who is "renowned for getting a fantastic deal for managers".
Van Gaal still has a season remaining on his three-year contract, while Mourinho has been out of work since paying for Chelsea's abysmal title defence with his job in December.
The Portuguese has repeatedly spoken of his plans to return to work this summer, and reviving United's fortunes would surely be a mouth-watering proposition for the self-styled 'Special One'.
United, a club synonymous with a swashbuckling, attacking style, managed a paltry 49 league goals - their lowest return for 26 years - and missed out on Champions League qualification to neighbours Manchester City on goal difference.
A first FA Cup win since 2004 was a welcome boost, but captain Wayne Rooney knows the campaign was far from good enough.
"He has been under pressure. I think we all have," Rooney said of Van Gaal.
"That's part of playing for Manchester United and managing Manchester United - it is a massive club.
"You have to set standards and we fell below them this season.
"But we have to make sure as players we get back to those standards and make sure we are back challenging for the main trophies."
Success is something former United midfielder and Chelsea assistant Ray Wilkins is backing Mourinho to bring back to Old Trafford.
"I think it is the right move," he told talkSPORT. "It is the only move for them. He will get them playing again and he will get them winning again.
"He is a winner - there is no two ways about it. When he goes to a club, normally he wins a big trophy within the first couple of years."