On Tuesday afternoon, Reynolds (adductor) was making a last ditched attempt to play against North Queensland on Friday night and is expected to be named.
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.
Duffy, just 22 and a former Cowboy, is readying himself to take control of the side alongside five-eighth Ezra Mam.
Experienced Arthars did a great job of replacing Walsh when he suffered a facial fracture just before halftime on Saturday night in the 26-12 win over Gold Coast when he switched from wing to fullback.
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' great 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.
His place is set to be taken by Blake Mozer, who is yet to play NRL this year.
Winger Josiah Karapani will return to the side after being dropped last week for disciplinary reasons.
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