The Telegraph reported that Williams had spoken to dietitians and the team's sports science staff to carefully plan his regimen over the next four weeks.
The newspaper reported that Williams was so respected at the Roosters that they could adjust their training schedule this month, allowing him to train after sunset instead of during the day.
Experts said that Williams' superb fitness would help him through the month.
The club's head of performance, Keegan Smith, was advising the champion forward on a diet that ensures he can maintain high energy levels. It will include breads, cereals, grain products, fruit, vegetables, meat, fish, poultry, milk, cheese, yoghurt and lots of water.
Williams - who married in secret last year - is not the first footballer to play NRL matches while observing Ramadan.
Former goalkicking champion Hazem El Masri, another devout Muslim, did the same thing at the Bulldogs back in 2009, the Telegraph reported.
"If you have the will and belief, you can achieve whatever you desire," El Masri said.
"Ramadan is a month of sacrifice. A month of dedication. People think of it as only abstaining from food and drink, but it's more than that.
"It's realising the position you are in. How lucky you are to have food and water to eat and drink."
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