The Colombia international has endured a stop-start campaign so far at Old Trafford following his season-long loan move from Monaco in September.
Having been ruled out for much of last season due to a cruciate ligament injury, Falcao remains around two weeks away from a return due to a calf problem picked up in training.
With the former Atletico Madrid man set to miss Premier League clashes with Arsenal and Hull City, Van Gaal stated that young striker James Wilson could be called on.
The Dutchman also added Falcao would not be considered for a starting place until proving his fitness, despite boasting a reputation as one of the world's best strikers.
"Wilson is a very good striker. He has to compete with these guys and it’s always difficult but when he wins this battle then he is a line-up player," Van Gaal said ahead of Saturday's trip to Arsenal.
"I have explained to my players, it’s not only a question of fitness but also you have to train with the group.
"Then you have to be better than the players who are on the list. I've said that before. Until now [Falcao] didn't train with the group so it's out of the question for him to be on the bench.
"I don't give any chance to players when they are not fit. Believe me, see my record. See the Dutch team, see all my expressions about fitness, you have to be fit. What's your name? It doesn't matter, you have to be fit.
"And now we have a lot of injuries. So they are not fit, I'm sorry. Then I have to manage with the other players. And we believe in these players. And we shall show it."
