Palace pushed hard to sign Amadou on deadline day, with the LOSC captain in London on Wednesday night. But agreement over a fee could not be settled.
Galtier stated: "Amadou? I will have an exchange over the day, he is certainly disappointed, it can be understood, but he is a very important player in the workforce, in the locker room and on the field. He's the captain.
"There may be a feeling of frustration that he will have to return quickly. We will help him. Ibrahim is disappointed, but there is a second part of the season to go.
"As I told him yesterday, although it was difficult for him to hear, the best is in front of him. With his agent, he put all the chances on his side by going over there.
"But you know, it's still a game of poker, in this case there was nothing done."