Fainu was last week found guilty of stabbing a youth leader at a church dance in 2019, before being denied bail and placed behind bars while awaiting sentencing.
Sea Eagles second-rower Haumole Olakau'atu raised eyebrows on the weekend when he gave a hand symbol of "61" after crossing for a try against the Gold Coast.
The number reference is believed to be a nod for the 2161 postcode in which he and Fainu grew up together, having been close since childhood.
Former Manly prop Addin Fonua-Blake also did likewise while playing for the Warriors.
NRL CEO Andrew Abdo confirmed on Wednesday the integrity unit had spoken to the clubs, particularly after the postcode gang wars in Sydney in recent years.
But Walker said Manly players would continue to stand by Fainu and should be able to back him in any way.
"Haumole and Nas have been best mates since they were little kids," Walker said.
"I would interpret that (symbol) to something completely different to someone that wouldn't be a part of that close-knit group.
"That could be anything from when they were eight or 10 years old.
"That's just Haumole showing his support behind him, which he needs because for the last few weeks we talk about mental health.
"This is a kid that was touted to be the next superstar and turns have taken the wrong way for him.
"As a playing group, we're showing as much support as we can."
Walker also claimed it was unfair to compare the celebrations to the decision of seven Manly players - including Olakau'atu - to not wear the rainbow jersey against the Sydney Roosters on religious grounds.
"I just think it's their choice (to support Fainu)," Walker said.
"That's what the whole inclusion jumper was about. It's a choice of yourself and what you want to support.
"That (symbol) is a choice that he (Olakau'atu) has made for a best mate that he's had for the last 15 years.
"So I support him in that way because Nas supported me through a lot of stuff."
Manly's season has spiralled disastrously since the jersey saga, falling out of finals contention.
But five-eighth Kieran Foran was adamant on Thursday they were not a split group after the jersey saga.
The club also took another hit on Thursday, with stand-in fullback Reuben Garrick ruled out for the final three rounds with a shoulder injury.
The results have piled pressure on coach Des Hasler, who is not guaranteed an extension into 2024 without a finals finish.
"I don't think anyone's better suited to coach this footy club than Des Hasler," Foran said.
"If the club's smart they'll hang onto him for as long as he wants to coach."
