The 23-year-old complainant is reportedly reluctant to make an official complaint and Queensland police confirmed none had been lodged.
"He came up from behind me and pulled my hair quite hard and yanked my head back," she said.
"I had a sore neck all day yesterday."
The incident is the latest in a long line of controversies to have marred the 23 -year-old's career.
He was fined $20,000 by the Broncos last year following allegations he abused a female staff member in a drunken incident at the Normanby Hotel in Brisbane when he was refused service.
He checked into a rehabilitation facility in Thailand at the end of the NRL season.
Before arriving at Brisbane, Roberts was released by South Sydney in 2012 after contract breaches, and then suffered the same fate at Penrith when a number of behavioural issues allegedly culminated in him smashing a taxi window in 2014.
He was thrown a lifeline by Gold Coast later that season and became one of the Titans' best players, before a contracting error on the club's behalf saw him depart for Brisbane last year.
The latest news comes just a day after his former Titans teammate, David Mead, claimed he had seen a more mature Roberts during his own shift to the Broncos.
"I've noticed an improvement in him as a person," Mead said on Monday.
"Obviously he's got a lot of good people around him here at the Broncos and he's very well looked after."
