The veteran striker missed training for a second day on Tuesday as his teammates took part in a double session at Fratton Park.
The reason for Kanu’s action is yet unclear to the club which he led to an FA Cup victory in 2008.
Administrator Trevor Birch said, “Kanu is back in Nigeria, that is the understanding from his legal adviser, who I have been speaking to. I don’t actually know why he hasn’t come back. You will have to phone him and ask him.
“What I do know, though, is we have not reached a compromise and he was due back on Monday along with the rest of the contracted players. Then he just didn’t turn up.
“Kanu must turn up for training, or this is a breach of contract.
“Whether it is sufficient enough to terminate his contract I don’t know at this stage, we will have to wait and see.
“He will have to be disciplined, though. What we intend to do is an internal matter. I cannot talk about that.
“However, if it is a continued absence we will have to bring in the PFA.”