United have failed to add to their arrivals of Luke Shaw and Ander Herrera, despite repeated links with Artuto Vidal, Mats Hummels, Daley Blind, Angel di Maria and Marcos Rojo.
While United have been slow in their attempts to reinforce their squad, Premier League rivals Manchester City, Liverpool, Chelsea and Arsenal have splashed the cash.
However, Van Gaal insisted there is still plenty of time to complete deals before the transfer window closes on September 1.
"I wanted to assess my team. I can judge only when I am the coach and I transfer my philosophy and know how they perform," the Dutchman told reporters on the eve of United's Premier League opener at home to Swansea City on Saturday.
"So that's what I am doing. I think that is honest. We have to wait and see, because you can buy a player in 24 hours, believe me. That's not a problem."
Van Gaal also reiterated his calls for patience as he attempts to overhaul the club.
The former Netherlands boss has overseen a change of formation, with a 3-5-2 system adopted throughout an unbeaten pre-season.
Van Gaal's tactics seem to have worked wonders up until this point but the 62-year-old warned there could be hiccups along the way.
"I cannot change everything [straight away]," he said. "I have to adapt to the culture. It's a process and we have to make steps.
"Sometimes you fall and you have to make another big step. That's the process but you are not champion in October. You are champion in May. I have another philosophy. I have another way of dealing with players to normal coaches.
"I'm not concerned where we might be [if we have a slow start] and I've said that in my meetings with [Ed] Woodward and the Glazers."
