According to the stuff.co.nz website, Williams, who on Tuesday confirmed he will fight South African heavyweight Francois Botha in Brisbane on November 24, is expected to finalise a one-year deal with the Roosters while in Australia for the bout.
However, he will then return to Japan to continue his stint with Panasonic Wild Knights before joining the Roosters in February.
But after recently meeting with Williams in Japan, Robinson is confident the New Zealand superstar will be fully focused and ready to play when he returns.
"He is a true professional in the sense that he is clear about the moment and what he has to do right now," Robinson said.
"He is also very clear about his training and the way he lives - not just the way he plays. They were the things that were impressive.
"It is incredible the way he is training and preparing over in Japan, and he is about to prepare for a fight so he is going to be ready physically.
"It is just a matter of re-adapting to the game. But I think he has played league for about 15 years."
Williams said he did not do the full pre-season training with his Chiefs team-mates in the lead up to this year's Super Rugby competition because he was fighting for the New Zealand heavyweight title, and it did not affect his form.
"I had a fight and that was eight weeks build up and I slotted back
into footy two weeks before the first game of Super rugby and my
fitness levels and everything were better than a lot of the boys,"
Williams said.