The Broncos play in-form Wests Tigers away on Saturday night, with the make-up of their side in flux and up to 11 top-30 players either unavailable or in doubt..
Their woes are mounting by the day. Riki's issue came to the fore at training on Monday when he did gym work before limping towards the training field to watch his teammates.
On Monday bench forward Aublix Tawha had surgery on an eye socket fractured while playing Hostplus Cup for Souths Logan on Saturday.
Hooker Blake Mozer is also out for six weeks with a broken jaw, while fullback Reece Walsh is sidelined with a facial fracture.
Hooker/half Ben Hunt (MCL) is unavailable, while prop Ben Te Kura, who has not played NRL this year, was granted six weeks' leave to attend an NFL training camp. Outside backs Delouise Hoeter (broken fibula) and Grant Anderson (MCL) are also unavailable.
There was good news on captain Adam Reynolds, who trained well after missing the 35-31 loss to North Queensland with a groin injury.
The Broncos debated whether to challenge Carrigan's grade-two careless high tackle charge on Cowboys centre Tom Chester, but decided not to risk losing their star forward for an extra week.
New Zealand international Xavier Willison, who has been coming off the bench, put his hand up to fill the Carrigan void at lock.
"If I am called upon then I am definitely ready," Willison said.
"Pat is a big loss. He does the big plays for us, which is what a leader should do. He definitely leads by example on-field and off-field.
"I am just focusing on getting myself right. It is a next-man-up mentality."
Willison, known simply as "X", came of age last year in the club's title win and built a reputation for his uncanny ability to come up with big plays in big games, as he did in the preliminary final win against Penrith.
The Broncos are set to give 20-year-old hooker Cameron Bukowski his NRL debut.
Bukowski is the fifth-choice hooker, but the Broncos also have dummy-half Billy Walters on the long-term injury list due to the ACL rupture he suffered last year.
Willison said Bukowski, who has been a star for Wynnum Manly in the Hostplus Cup, had more to offer than just his noted footy smarts.
"He is a pretty good defender, so it will be good to rub shoulders with him for the first time," Willison said.
"He is pretty crafty out of nine, so I am looking forward to what he can do."
Late on Monday the Broncos were still in talks with the NRL about overturning a controversial category-one concussion handed to hooker Cory Paix against the Cowboys, which effectively ruled him out of the Tigers clash. Paix passed his HIA and was flabbergasted about the decision.