Louis van Gaal has issued an ultimatum to Radamel Falcao that he has to prove himself at Manchester United.
Falcao has scored three goals in 13 appearances since arriving on loan from Monaco.
"That is not for you, it's not for the media. It's for between a player and his manager. I'm sorry," said van Gaal.
"You have to wait and see, because when I say that a part of my line-up is known and then I make it easy for my opponent, and I don't want to make it easy."
When asked about the intrigue of Falcao's high-profile arrival at Old Trafford, Van Gaal replied: "For the manager that is not so interesting. For the manager it's the quality of the training sessions, the quality in his performances in matches, and he has to compare.
"You have a gameplan. I have already explained it after the match against Southampton, and it is always the same explanation.
"If a player costs £95 million or £5,000, it's not any difference for me. It's difficult to understand for you, I believe. Because it is never the second question or the third question but it's like that. You have to prove yourself.
"And a player of £95m has to prove himself also, and when I'm not like that maybe he has less motivation, so I have to be like that, but for the outside world it is difficult."