On Tuesday afternoon, Reynolds (adductor) was making a last-ditch attempt to play against North Queensland on Friday night and was named at No.7.
He ran with a trainer to test his groin before training and has not given up hope. Reynolds will rest up and see how his injury recovers during the week before a final decision is made.
Duffy, just 22 and a former Cowboy, is readying himself to take control of the side alongside five-eighth Ezra Mam if Reynolds is ruled out.
Experienced Arthars switched from wing to fullback superbly to replace Walsh when he suffered a facial fracture just before halftime on Saturday night in the 26-12 win over Gold Coast.
Arthars, who has been playing alongside Duffy in Queensland Cup at Souths Logan, said he was ready to take his chance.
"I have been playing Cup with Duff. If he does get a shot it is going to be awesome for him," Arthars said ahead of his 100th NRL game.
"He is just a very good organiser, very vocal and good at steering the team around. If Reyno is not healthy then that is something Duffy can easily fill in and do."
Walsh is one of the superstars of the game but Arthars is not going to try to emulate his style of play.
"I don't feel the pressure. Obviously we are two different players and I just want to bring my strengths," Arthars said.
"I am sure the boys will have faith in me and that is something I want to repay to my teammates and to Madge (coach Michael Maguire) for picking me and trusting me."
Teammates have spoken of Arthars' keen organising ability at the back and his strong ball running as key traits.
"They are the areas I really want to focus on if I am going to be playing fullback. I like to bring a lot of energy and talk a lot around the club," Arthars said.
"If I am playing fullback that is something I need to be able to do and something I am comfortable with."
The Broncos will also be without half/hooker Ben Hunt after he suffered an MCL injury against the Titans that will keep him out for six to eight weeks.
Hunt's place on the bench is taken by Blake Mozer, who will play his first NRL game this year.
Broncos hooker Cory Paix, who spent all of 2024 in Queensland Cup, said Mozer had bided his time and was a class act.
"I have been through those times. Patience is a key, really," Paix said.
"You just have to be ready because you never know when you will be called upon. Blake has all the ability in the world, he just has to be himself."
Winger Josiah Karapani returns to the side after being dropped last week for disciplinary reasons.
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