Physio Jon Fearn claims that had the infection not been operated on promptly Williams career could have been under threat.
"The infection was inside the joint which could have been potentially career threatening if we hadn't picked up on it quickly enough, because the infection can corrode the joint's surfaces," explained Fearn, speaking to readingfc.co.uk.
The Welshman missed Saturday's FA Cup tie at Walsall, but instead of getting better the injury worsened, prompting club officials to rush Adie into hospital for an emergency operation on Monday morning.
"It's still early days but Adie could be out for three or four weeks," added the Royals physio.
"When the injury worsened over the weekend, it became clear to me that there may be an infection in the knee which had to be looked at quickly.
"We went to the hospital on Monday morning and Adie had a procedure to analyse the fluid in the knee. He also had his knee washed out through an arthroscopy, and will stay in hospital for a couple of days on intravenous antibiotics to clear up the remaining infection and make sure we kill it."
Twenty-six year old John Mackie is expected to cover in the heart of the defence alongside Steve Brown until Williams is ready to return to the side.