The all-British fight had looked set to take place in Saudi Arabia in August.
But it fell through when Deontay Wilder's team won an arbitration hearing stating the American had a right to a third fight with Fury.
"It might not be December or even next year," said Bunce.
The much anticipated fight between Fury and Joshua would have seen the pair contest all four world titles for the first time in the sport's history.
Fury is the WBC champion while Joshua has the WBO, WBA and IBF belts.