Mali midfielder Diakite joins QPR on loan
Diakite, 23, had been allowed by Mali coach Alain Giresse to fly from Gabon, where he is playing in the Africa Cup of Nations, to London to sign his contract.
"It will become a permanent transfer if the London club stay in the Premier League," Nancy said in a statement.
QPR, who are two points above the Premier League relegation zone, will have to wait to see when Diakite can join them as it will depend on how far Mali get in the Africa Cup of Nations which runs until February 12.
Mali are third in their four-team group with three points from two games, level on points with second-placed Guinea with one Group D game to play.
The top two teams in a group go through to the quarter-finals.