The Red Devils will head to Palace sitting sixth in the table, two points clear of seventh-placed West Ham United, potentially needing a result to secure their spot in next season's Europa League.
According to the Daily Mail, Ten Hag and Van der Gaag arrived in London via a private jet on Wednesday, and the duo could be in the stands for Man United's match with Palace on Sunday.
The report claims that the duo will hold a meeting with colleagues over the next 24 hours, with Steve McClaren also set to return to Old Trafford as part of the new coaching team.
Man United will post their worst ever points total in a Premier League campaign regardless of whether they manage to pick up all three points away to Patrick Vieira's side this weekend.
The 52-year-old led Ajax to this season's Eredivisie title, and he steps down from his role with the Amsterdam giants having delivered three league titles and two Dutch Cups during a successful spell.
Man United, on the other hand, have largely struggled since the departure of legendary head coach Sir Alex Ferguson, and Ten Hag will be tasked with making the club competitive once again for the major trophies.
As it stands, the English giants will be playing in the Europa League next term, but a win for West Ham at Brighton on Sunday would leave Man United needing to collect all three points to avoid dropping into the Europa Conference League.
"There's a lot of work to be done there [at United]. Of course. There's a lot of work at every club. A manager's job is especially focused on the preparations for next season. And there's a lot of work to be done in that regard," Ten Hag said after Ajax's final match of the campaign against Vitesse.
"Regarding the staff, there are several things that need to be organised. And also regarding the team and over the next several days, or actually as of tomorrow [Monday], we will be focusing on that intensively."
A new midfielder and centre-forward will also be targeted in the upcoming market, but the club's failure to qualify for next season's Champions League has harmed the club's transfer budget.
Man United's wage bill will be significantly trimmed this summer, meanwhile, with the departures of Paul Pogba, Jesse Lingard, Edinson Cavani, Juan Mata and Nemanja Matic on free transfers. body check tags ::