Fairfax reported Williams's one-year deal with the Roosters hadn't been ratified by salary cap auditor Ian Schubert.
The NRL confirmed more information was needed to bed the deal down.
"We are waiting for some information that has been requested from the club," NRL spokesman John Brady told Fairfax.
"Everyone is aware of the need to process this as soon as possible."
Clubs have until Friday to lodge signed statutory declarations that they comply with the salary cap.
Williams hasn't played in the NRL for five years, playing rugby union in France and New Zealand during that time.
Roosters boss Brian Canavan believed the issue would be sorted in the coming days.
"There's a bit of paperwork to transpire," he said.
"The registration is conditional on some paperwork to be supplied. There's a bit more detail (required) in some of the correspondence we sent through, which is virtually assembled now."
