Reports were circulating on Tuesday that the New Zealand superstar's fitness was in doubt for what's shaping up as the most talked about curtain-raiser in years.
Williams has been battling a knee problem and also underwent surgery to repair a torn prectoral muscle late last year.
However, Maguire said his side would not alter their preparations for the game, which is close to a sell-out.
"I don't have information on it, but I have heard the same stories, but we are very focused on what we have to do and that won't change," Maguire said.
"We are very aware of what he can do. He is a great player and has achieved a lot.
"But at the end of the day, all we are focusing is what we can control.
"I was really pleased with the pre-season. The boys worked really hard over the three months but that is behind us now and we need to put it into practice."
Maguire will name his side on Tuesday afternoon, with former Melbourne prop Jeff Lima in line for his debut.