The captain's armband for the 2014-15 campaign is up for grabs after former skipper Nemanja Vidic joined Serie A side Inter on a free transfer at the end of last season.
Robin van Persie and Wayne Rooney are the reported frontrunners to lead United, and the Dutchman is favourite to get the nod having captained Van Gaal's Netherlands team at the FIFA World Cup in Brazil.
However, speaking at his official unveiling on Thursday, Van Gaal said "all the players were possible candidates".
"I have to know them and therefore I use four, five, six weeks, dependable if I'm out already after four weeks but it could be two months," Van Gaal told reporters at United's training base.
"For me the captain's role is very important and therefore I need time and sometimes I didn't have the time, then I have to make quick decisions but quick decisions are not always good.
"So I use my time for it because I think the captain of a team for me is very important."
