Addo-Carr was pulled over for a random test while driving in Newtown in Sydney on Friday night, before police allege he returned a positive wipe test for cocaine.
He is now awaiting the results of an oral fluid sample.
The incident comes after the final year of Addo-Carr's last contract at Canterbury was torn up in late 2024, after another positive roadside drug test.
Parramatta confirmed on Saturday afternoon they were aware of an incident involving the 31-year-old, who finished this season with eight tries from 23 games.
"The Parramatta Eels are aware of an alleged incident involving Josh Addo-Carr," the Eels said in a statement.
"The club has notified the NRL Integrity Unit and is co-operating with the appropriate processes, as well as providing welfare support to Josh and his family.
"Parramatta Eels will not be commenting further until the matter has been finalised."
The NRL's illicit drug policy states that any player who returns a positive drug test receives a suspended fine and must undertake a mandatory treatment program.
A second offence is met with a 12-match ban and fine, along with further treatment. There is an option for contract termination.
Whether police roadside tests fall under that policy is not entirely clear.
But regardless, the former Melbourne and Canterbury star will face an uncertain future if an oral test conducted by police also returns a positive sample.
The representative winger is only contracted to Parramatta until the end of next year, and if charged and found guilty of the offence he would likely face an integrity unit ban at the very least.
In 2024 Addo-Carr maintained he had not knowingly ingested recreational drugs, before the Bulldogs decided to rip up his contract.
He was handed a four-match ban by the NRL integrity unit and a $15,000 fine.
The five-time Australian representative was also fined $682 and suspended from driving for three months following the incident.
Police confirmed on Saturday they had pulled over a 31-year-old at 11.10pm (AEST) on Friday, and he had passed a roadside alcohol breath test.
"The driver underwent a preliminary drug wipe, which allegedly returned a positive indication for cocaine," a NSW Police spokesperson said.
"An oral fluid sample was obtained and sent for further analysis.
"The investigation is ongoing, as police await the results of the forensic analysis."
Addo-Carr had been included in Australia's preliminary 40-man World Cup squad.
His selection in the final group now appears unlikely.
It is unclear if the World Cup games would count towards any ban.
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