In a video posted to TikTok, a Penrith supporter calls out to Walsh as he leaves the fan day at Circular Quay in Sydney on Thursday afternoon.
According to the clip's caption, the supporter told Walsh that Panthers prop Moses Leota was "gonna take his head off" in Sunday's decider between Penrith and the Broncos.
The brief video ends with Walsh telling the fan "I'll take your mum's" and walking away.
The NRL integrity unit told AAP they had been made aware of the incident but that no investigation had yet been launched.
"The NRL integrity unit is aware of the matter," a spokesperson said.
Brisbane coach Kevin Walters defended Walsh after the video surfaced on Friday afternoon.
"It's difficult for 'Walshy'," he told Triple M.
"You either love him or hate him and most people thankfully love him.
"We're in a bit of foreign territory here in NSW. So there's going to be some people out there that are quite jealous of Reece and how he plays the game and his looks and all those things.
"That's something he's going to have to get on top of for the rest of his career.
"You can't take Nerang out of the Nerang boy."
Walsh has become one of the NRL's most popular stars in his first season since joining Brisbane from the Warriors, but has previously run afoul of the league for his fiery temperament.
He received a three-game ban for swearing at referee Chris Butler during a match against Gold Coast in late June, ruling him out of contention for the Dally M Medal.
He was also sent off during the second State of Origin clash after a passionate exchange with NSW five-eighth Jarome Luai in which both men head-butted each other.
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