Adam Reynolds won't play for Brisbane against Penrith in round three's grand-final rematch, while prop Payne Haas is also in doubt, Kevin Walters says.
Reynolds sustained a medial collateral ligament (MCL) strain and Haas injured a knee in the 28-18 win over South Sydney on Thursday night.
Broncos captain Reynolds will be replaced by 24-year-old half Jock Madden for Thursday's away clash with the Panthers.
Reynolds and Haas were in rehab at training on Sunday, and neither took part in the team session.
"Payne has been named but we are not 100 per cent sure he will be playing yet," Walters said.
"He has still got a bit of a problem with his knee. He's had some scans and there wasn't too much there, but ... he is still not right to go at this stage.
"Reyno won't be playing and won't be named. He is out."
If Haas is unable to play, Walters said prop Xavier Willison would come into the 17 to face the Panthers.
Fullback Reece Walsh sustained a minor injury in the win over the Rabbitohs and was in a no-contact red training bib on Sunday.
After doing his own warm-up, Walsh took part in an opposed session against Broncos affiliate club Wynnum-Manly.
"Reece is fine. He just has a bit of a cork. He will be right," Walters said.
Former Wests Tigers playmaker Madden featured in five NRL games for the Broncos last year when Reynolds or No.6 Ezra Mam were out injured and handled himself well.
"Every time Jock has had an opportunity he has played really well for us, so we expect no different on Thursday night in Penrith," Walters said.
"It is a great opportunity for Jock to showcase his skills. He is a different player to Reyno but an equally important member of the team.
"He is still maturing and we have a lot of confidence in him and the skillset he brings to the club."
Walters said the Broncos would err on the side of caution with key players such as Reynolds and Haas at this time of the year.
"We are two rounds in and we are keeping in mind the health and welfare of our players," Walters said.
"We are making sure if they do take the field they are in a position where they can do their roles capably.
"Each injury is different and each player is different. It is player welfare more than anything."
