The 19-year-old is being chased by a flock of clubs across Europe, although Galtier said that there are three in particular showing serious interest.
"I do not know if he has already had offers," he told Le Progres. "I know that three clubs are following Kurt very closely. Will they make offers when the window opens? Anything is possible.
"As coach I always want to keep my good players. But there are obligations before the summer because there are budgets to do.
"Losing a big player in winter? We have to be careful because it is not expected. But now £11m is a lot of money – but there is a second half of the season to think about."
Chelsea are said to be leading the race for the French Under-21 international.