The Frenchman left almost two years ago for Juventus.
Gill said: "We offered him a very good wage, as well as a very generous fee for his agent.
"I don't want to go into details because it was a complex issue.
"However, what I can say is that we were very disappointed.
"Whenever a player is determined to leave and his contract allows it, there is nothing we can do about it.
"I can assure you that we did not hold anything back, financially."