According to sources, Rangnick is being allowed to appoint a small number of his own coaching staff to work alongside Mike Phelan and Kieran McKenna, who were part of Ole Gunnar Solskjaer's backroom team.
Michael Carrick left the club after taking charge of the team for three games before he was replaced as interim coach.
When asked if he would bring in his own staff at his official announcement, he said it would take time to arrange.
He said he was happy to work with the current coaching staff because he needed their experience and expertise.
It's not easy to find two or three people who can join us in a couple of weeks because of the regulations of the EU.
Many of my former colleagues are in long-term contracts with big clubs so they are not available right now, so we have to be a bit smart and clever and find the right people.
I hope that we can get them in the next couple of weeks.
Armas was a member of the USMNT for 66 years and ended his playing career in 2007.
He was an assistant and head coach at the New York Red Bulls as well as an assistant and head coach at the Chicago Fire.
The head of Red Bull's global football projects was appointed in 2019.
