Jose Mourinho says he will not try to sign players who will only use interest from Manchester United to benefit their own situations.
The United boss was reluctant to discuss the end-of-season transfer window in great depth with four months of the season still to play.
But he reiterated he has only given the club's board realistic targets and would not go for unattainable players who use United's approaches to improve their contracts with their current clubs.
Gareth Bale, Neymar, Sergio Ramos and Cristiano Ronaldo have been among the big-names chased by United in recent years, only for them to later sign new deals in Spain.
"Of course I know what I want," Mourinho said ahead of United's trip to play Premier League champions Leicester City on Sunday.
"Until the summer I have nothing to tell you, I will work with my players and I know them better now than I did about seven months ago.
"But I think we need to be realistic and I know what the impossible targets are. I don't like my club to participate in impossible deals.
"It is a waste of time. It is a gift to agents of these impossible players to have United interested in them because it helps them to improve their own situation - but it is not good for us at all.
"I am very realistic, very objective. My board knows what I think our needs are.
"From now until the summer I am just focused on our players, our targets and our fans. To be speaking about the transfer window in February makes no sense at all."
United travel to Leicester having drawn three straight top-flight matches, but Mourinho feels their comparative struggles to the likes of Chelsea and Liverpool are to be expected due to their rivals' extra time between fixtures.
"If a player has fatigue, there is no fatigue," Mourinho said of Chelsea and Liverpool.
"If the player has a small injury, there is no accumulation. So in the end the team, by the tactical point of view, becomes better than the others that don't have the same time to work.
"You always have four days in a week to work when you have one game a week, it accelerates the tactical understanding.
"But it is a plus that I wouldn't like to have because I always prefer to play in Europe even if it is the Europa League."