The Posh manager confirmed there had been disagreement with Gnakpa over the terms of a new contract.
"We made him a good offer as he has played well for us this season, but if players think we will meet all their demands then they are wrong," he said.
"I thank him for all his efforts but he won't be here next season."
Ferguson also confirmed Rene Howe will return to Posh after a successful loan spell at Rochdale.
