Coates told delegates at an Olympic forum in Sydney that construction had not started on some venues, infrastructure was majorly delayed, and water quality was already a concern.
In an unprecedented move, Coates said the IOC would be forming a special task force to help with preparations but said the situation was still critical on the ground.
"The IOC has adopted a more hands-on role, it is unprecedented for the IOC but there is no plan B. We are going to Rio. We have become very concerned, they are not ready in many, many ways. We have to make it happen and that is the IOC approach, you can't walk away from this," said Coates.
Coates was paraphrased to have said that it is worse than preparations in Athens in 2004, which were plagued with construction and service delays that were only pulled together just in time.