The Dutchman dodged the cameras at the main gate but was shown in pictures on the club's Twitter feed alongside his assistant manager Ryan Giggs and executive vice-chairman Ed Woodward.
Van Gaal was due to meet those players not on a post-World Cup break as well as the rest of the club staff.
He has taken up the reins only four days after guiding Holland to third place at the World Cup in Brazil, eschewing a break himself.
And the 62-year-old, United's first manager from outside the British Isles, will have no time to ease himself in.
On Thursday he will be officially presented at a press conference at Old Trafford at 3pm before jetting off to the USA on Friday for the club's pre-season tour.
United will play matches against the Los Angeles Galaxy, Roma, Inter Milan and Real Madrid, while Van Gaal's Old Trafford debut will come in a friendly against Valencia on August 12.
Four days later United will open their Barclays Premier League campaign at home to Swansea.
A fast start will be a major priority for the new boss as United look to bounce back from last year's seventh-placed finish, which cost Van Gaal's predecessor David Moyes his job.
There is plenty for Van Gaal to get his teeth into, not least whether he wants to go into the transfer market to add to the summer signings of left-back Luke Shaw and midfielder Ander Herrera.
Defence appears to be an area of priority given the departures of Rio Ferdinand and Nemanja Vidic, while Van Gaal must also decide whether a number of players have a future at Old Trafford.
United have been heavily linked with a bid for Juventus midfielder Arturo Vidal, a star of the World Cup with Chile, and speculation increased when Antonio Conte stepped down as Juve manager on Tuesday.
But at a press conference to unveil Massimiliano Allegri as his successor on Wednesday, Juventus insisted Vidal is not for sale.
Club administrator Giuseppe Marotta said: ''Vidal is a Juventus player and we have never put him up for sale. A lot of clubs have asked for him but we have never sat down to negotiate.
"We want to keep him. Vidal has expressed many times how happy he is to remain in Turin and, if that is confirmed, we will be happy to continue together."
Speaking in Chile earlier this week about the potential of a move to United, Vidal said: "I'm already at a great team, Juventus, so I will be just as calm if the Manchester United option falls through."