Reynolds had scans on Saturday on the injury he suffered in the 40-18 loss to the Sydney Roosters on Friday night.
"Adam's scan showed a ruptured bicep. He will have surgery early this week and be out for 12-14 weeks," Broncos head of performance Dave Ballard said.
That will leave the 33-year-old conductor and 2014 premiership winner out of action until at least round 21.
Madden, the club's back-up half, had a minor pectoral injury in round eight against Wests Tigers while playing five-eighth.
Walters said Madden was racing the clock to be fit for next Friday night's away clash with Parramatta.
Broncos coach Kevin Walters gives Jock Madden some advice at training. (Darren England/AAP PHOTOS)
Utility Tristan Sailor is an option if former Tigers half Madden does not recover, but the Broncos are backing the 24-year-old - seen as the successor to Reynolds - to step up in the wake of the skipper's injury.
"We would prefer for guys to not get injured but it gives us an opportunity to have a really good look at Jock for the next 12 or 14 weeks," Walters said.
"It was a one-to-two-week injury but I haven't had a chance to talk to the doctors about Jock and his return. He would be an outside chance against Parramatta.
"(Sailor) could play a role there for us, certainly. He has got a good football IQ.
"We have been defending him in the front line and he has been doing that at Queensland Cup level. We have got some options but will let the dust settle over the weekend.
"We have got good depth ... We will get Adam back I am pretty sure before the year is out, and also Jesse Arthars."
Walters ruled out switching fullback Reece Walsh, who had a poor game against the Roosters, to the halves.
"We will leave Reece at fullback," the coach said.
Winger Arthars broke his jaw against the Roosters and was taken to hospital. He is set to be replaced by veteran Corey Oates.
Jesse Arthars being tended to after breaking his jaw against the Roosters. (Jono Searle/AAP PHOTOS)
Arthars had surgery on Saturday and will miss six weeks of action, Ballard added.
"We will find out what we are made of. Such is life with footy," lock Pat Carrigan said of the growing injury list.
"This happens with a lot of teams and ... it is the next man up.
"We have got a lot of depth at our club and I am confident whoever plays there will do the job.
"There is a footy team here. We just have to iron out a couple of things."
Brisbane had some good news on Saturday, with winger Deine Mariner avoiding a ban after being sin-binned for a late hit on James Tedesco.
