The Holland midfielder has skipped training as he pushes to join Juventus.
"Koopmeiners wants to move to Juventus," Gasperini told L'Eco di Bergamo. "The situation with him went very well until last week, then the player decided to go to Juventus, he already has an agreement, he feels stressed and has decided not to play or train with us anymore."
"With this attitude," he continued, "he cannot be useful either to the team or to his teammates. The club in turn has taken a very firm attitude, because it feels blackmailed by this situation. Different from the other times in which Atalanta has sold some valuable pieces to the big names."
Gasperini added: "I'm already loaded, on the starting blocks, and I wouldn't want to find myself dragging those who are still celebrating last season.
"We need locomotives, because in a week the season will start: either give them or take them. And we arrive in a much more difficult situation than we could have foreseen."