The Hoops are eager to tie down the Kenyan midfield powerhouse, who has recently attracted Premier League interest, but his agent has revealed that their extension offer is not enough.
"Victor has informed Celtic the contract offer fell short of his expectations. There were a number of aspects that fell short - he turned it down," said his representative Rob Moore.
"There hasn't been another offer. The ball is in Celtic's court."
Moore added: He said: "He is very happy with the job he is doing at the moment. He's a great professional and his commitment cannot be questioned.
"But it doesn't take a rocket scientist to work out that he lost great earning potential in the summer."