Eyebrows were raised when Manchester United boss Van Gaal sanctioned the sale of Old Trafford academy graduate Welbeck to one of his club's main Premier League rivals on transfer deadline day.
Van Gaal felt there was no room for the 23-year-old in his squad due to the presence of stellar attacking talent such as Wayne Rooney, Radamel Falcao and ex-Arsenal captain Robin van Persie.
Welbeck struggled to establish himself as a first-team regular at United after making his Premier League debut in November 2008, but has quickly become an integral part of Arsenal manager Arsene Wenger's plans.
And, speaking ahead of United's trip to the Emirates Stadium on Saturday, Van Gaal said he expected Welbeck - who has scored 10 goals for club and country this season - to take the greater opportunities on offer in north London with both hands.
"A player who plays in a fixed team develops better, so he takes all the benefit that he plays every week," the Dutchman told his pre-match media briefing on Thursday.
"That was the question mark with Manchester United. It's very good to see him doing what I thought."
Van Gaal has experienced a mixed start to life in the Old Trafford hotseat, winning just four of his opening 11 Premier League games.
The former Netherlands coach has been hampered by a raft of injuries in the early stages of his tenure, but has been boosted by the news that key men Angel di Maria and David de Gea are both fit after suffering injury scares on international duty.
Michael Carrick is also available after sustaining a groin problem while away with England, but United's injury list still makes for unenviable reading.
Daley Blind (knee), Marcos Rojo (shoulder), Jonny Evans (ankle) and Phil Jones (shin) are all definitely out, while Falcao (knock), Luke Shaw (groin) and Rafael (muscle problem) are doubtful.
However, despite his lengthy list of absentees, Van Gaal is relishing the prospect of pitting his wits against Wenger - for whom he reserved strong words of praise.
"It's the first time I've sat on the bench against Arsenal as Manchester United coach," he added.
"I've only played once against Arsenal with Barcelona [in 1999] - Wenger was on the bench. I admire the way they play because it's attacking and you play for the fans. I think that's nice."
While most of the pre-match media attention will be focused on Welbeck's first game against his boyhood club, United will arguably be more wary of another Arsenal striker.
Alexis Sanchez has been in blistering form in recent weeks, scoring nine goals in his last eight appearances for his club and Chile.
Just a point separates Arsenal and United in the table, although the London club will be confident of at least maintaining that narrow lead over their opponents having not lost a Premier League game at the Emirates since the opening day of the 2013-14 season.
Wenger can welcome back Mikel Arteta and Olivier Giroud, who are available after a hamstring problem and fractured leg respectively, but Mathieu Debuchy (ankle) and Laurent Koscielny (Achilles) remain sidelined.
The Frenchman also revealed on Thursday that Mesut Ozil is unlikely to play again until the new year due to his knee injury.
