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.
It comes after the final year of Addo-Carr's last contract at Canterbury was torn up in late 2024, after a 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 club 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.
Players are not named publicly upon recording a first strike.
A second offence is then met with a 12-match ban and a fine, plus further treatment. There is an option for contract termination.
It is understood that in roadside tests such as Addo-Carr's, it would likely be considered a strike if the fluid test returns positive for cocaine.
Whether Australia's World Cup matches could be counted towards a ban may also be up for debate, given Addo-Carr was in Australia's preliminary 40-man squad.
But regardless, if Addo-Carr's fluid test returns positive, the winger's playing future will likely be plunged into doubt, with his contract at Parramatta expiring next year.
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's integrity unit and a $15,000 fine.
The five-time Australian representative was also fined $682 and suspended from driving for three months.
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's latest matter comes just days after he was named Parramatta's community player of the year at the club's awards night.
He was also selected for the NRL community team of the year, and nominated for the Ken Stephen Medal.
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