Dutch newspaper De Telegraaf has reported that Van Gaal has agreed to take charge at Old Trafford after leading the Netherlands at the World Cup in Brazil this summer.
But United have told Sky Sports that they have not yet signed a new manager and will make an announcement when they have done so.
Van Gaal, 62, has reportedly held talks with United executive vice-chairman Ed Woodward and one of the Glazer brothers in the Algarve and agreed a deal to take over from axed boss David Moyes.
The current Dutch boss is United's number one target and club officials met with Van Gaal almost two weeks ago, according to the Dutch paper.
De Telegraaf said on Saturday: "The national coach late last night reached a deal with the top British club.
"The man who's the absolute number one to replace axed coach David Moyes will immediately take up the job when the Dutch XI is knocked out of the World Cup in Brazil."
Van Gaal is believed to have insisted the club terminate the contract of Moyes before holding further talks. But now with Moyes gone and a settlement agreed the club have pursued the former Bayern Munich boss, who is reportedly set to get around £82m (100m euros) to spend in the summer.