Arsenal comprehensively beat Man United at the start of October before the squad immediately jetted off with their respective national sides.
That meant van Gaal was left to dwell on the performance at United’s Carrington training ground.
The Dutchman revealed that him and the staff at United have been downbeat during the last two weeks.
“When you have more than two weeks [to think about it] it is awful when you have such a result,” van Gaal said.
“It has been an awful two weeks because before the last international break we lost against Swansea [City].
“It’s not only the players, it’s the staff, and my cook, Mike, because he has a big influence on the atmosphere in the canteen.
“So these are awful weeks, because you are constantly thinking about how it happened and you cannot manage it with your players, because that is what you have to do, but all the players were flying out.”
Everything that could have gone wrong against Arsenal went wrong and it was the worst possible way for United to head into the international break. They have a chance to put things right against Everton this weekend, although Roberto Martinez’s side will undoubtedly provide a stern test at Goodison Park.