The path was clear for the former Chelsea manager to be confirmed as the new United boss after Van Gaal was sacked Monday - the price of failing to get one of the world's biggest clubs into the Champions League.
Mourinho's agent Jorge Mendes was reported by British media to be in negotiations to tie up a deal.
It sets the stage for one of the sport's most intriguing characters to at last manage the Red Devils after a glittering career that so far features 21 major trophies, including three English Premier League crowns and two Champions League titles.
Mourinho was sacked by Chelsea in December after a miserable campaign marred by rifts with the club's star players that eventually became intolerable to owner Roman Abramovich as the team, champions just months earlier, languished near the relegation zone.
Now the colourful and controversial 53-year-old will hope to restore his reputation by bringing back the sparkle to United.
A casually-dressed Mourinho declined to answer reporters' questions as he left his London home and got into a car on Tuesday morning.
The BBC said the Portuguese manager's appointment was unlikely to be finalised Tuesday but was expected to be completed within the week.
For his part, Van Gaal said he was “very disappointed” to be sacked just 48 hours after leading United to victory in the FA Cup final against Crystal Palace on Saturday.
But United had finished fifth in the Premier League and thereby missed out on a lucrative Champions League place, which proved the final straw for the club's US-based owners.
The Glazer family didn't let United's first piece of silverware since the 2013 retirement of legendary boss Alex Ferguson stop them from wielding the axe on 64-year-old Van Gaal.
The Dutchman cleared out his office at United's Carrington training ground on Monday after talks over a settlement for the final year of his three-year contract - worth a reported £6.4 million ($9.2 million, 8.2 million euros) per year.
The Daily Mirror newspaper reported that Mourinho called Van Gaal in the last few weeks to warn him that United had sounded him out about the Old Trafford job.
Mourinho worked under Van Gaal at Barcelona in the late 1990s and made the call to preserve their long-standing friendship, the tabloid said.
The Times newspaper said it understood Van Gaal would have left United without a pay-off - as he has at previous clubs - had the Red Devils handled his dismissal better.
It said he finally agreed a severance package of £4.55 million.
United goalkeeping legend Peter Schmeichel believes Mourinho is the right man to get the club back on track.
“They have a guy that is supposed to be the biggest manager in the world, the one that really could save Manchester United,” the Dane told the BBC.
“It has been a brave decision but one that is long overdue.”
Mourinho seemed destined to manage United ever since his Porto side eliminated Ferguson's men from the 2004 Champions League.
He thought his time had come when Ferguson retired in 2013, but concerns over his volatile nature prompted United to turn to the more reserved David Moyes instead.
But with that move proving a disaster and Van Gaal faring little better, United's powerbrokers have decided to take a chance on Mourinho.
Mourinho will hope to have significantly improved an unbalanced and often lacklustre United squad by the time the new season begins in August.
Outgoing Paris Saint-Germain forward Zlatan Ibrahimovic, Sporting Lisbon midfielder Joao Mario, Everton defender John Stones, Chelsea midfielder Nemanja Matic and Atletico Madrid forward Antoine Griezmann are reportedly among the names on his wanted list.
But Mourinho might also have to deal with scepticism from the squad at Old Trafford after a report that some senior players have already expressed concern the tactically defensive coach might prove too similar to Van Gaal, whose dull tactics frustrated United fans.
If he can rebuild the confidence of his squad and make United champions for the first time since 2013, Mourinho may regard it as his finest achievement yet. – AFP
Original source: United gig is Mourinho’s dream job