Moyes' dismal ten-month tenure at Old Trafford was brought to an end in April after losing 2-0 at the hands of his former club Everton, and Netherlands boss van Gaal will now take over the reins after he has completed his duties with the Dutch side at the World Cup in Brazil.
Moyes' departure seemed to end United's interest in a number of players ahead of the summer transfer market, and one of those was Inter's Colombian international Guarin, who is currently in Brazil for the World Cup. Yet speculation this morning suggests that this isn't the case, and that the 27-year-old could still end up a United player.
This morning, The Mirror picked up on new speculation in the Italian press, which suggested that whilst Bayern Munich's Toni Kroos and Roma's Kevin Strootman have been the names most strongly linked with moves to Old Trafford, it could well be Guarin who is van Gaal's primary target.
The report suggests that United are willing to bid up to £18m in order to land Guarin - and that Inter are unlikely to reject such an offer.
Adding a midfielder has to be van Gaal's primary concern once he assumes his role at United, after poor displays from the likes of Michael Carrick, Tom Cleverley and £27.5m flop Marouane Fellaini. Guarin may not be the big name signing that United fans are looking for, particularly having not even been selected in Colombia's starting XI to face Greece on Saturday, with Carlos Sanchez and Abel Aguilar favoured.
Yet Guarin is experienced, strong and can pack a real punch from long range - as his recent goal against Jordan demonstrated. And after a season of below-par midfield performances, Guarin could be the injection of athleticism that United need in the middle of the park.