Louis van Gaal conceded the make-up of his squad may see him move away from the 3-5-2 formation he had favored previously.
"I started with another system," he said. "Now we have bought players in and you have to look at their qualities.
"I don't think any player is fixed. Only the captain [Wayne Rooney] has more privileges.
"Falcao is a very good striker and I like [Robin] Van Persie. Then we have Rooney, [Adnan] Januzaj and [James] Wilson. We have five players for two positions.
"Januzaj has to compete with very strong strikers. When we play 4-3-3 he should have more chances to play."
Via FourFourTwo