The Colombia international joined the Red Devils on loan from Monaco at the beginning of the season, but has managed just three starts and four substitute appearances in the Premier League this term.
The 28-year-old is now expected to again be on the bench when United travel to Southampton on Monday, with Van Gaal unwilling to change his ‘philosophy’ to please one squad member.
The Dutch tactician said: “Falcao needs match fitness. He can only play for 20 minutes.
“I have selected him despite that but the rhythm of the game in the Premier League is the highest.
“It would be a better contribution if he played with the second team but I cannot do that because on Tuesday (Wayne) Rooney was injured for the match against Stoke.
“I had to adapt to the needs of selection. I am not interested whether he (Falcao) is unhappy being on the bench. He has to follow my philosophy. I am here because of that.”