Boyd's future has come under scrutiny after underwhelming 2019 form and a revelation that the 32-year-old will need to play 15 games next year to ensure he sees out his current contract until the end of 2021.

Two-time Broncos premiership player Johns is the first to admit that Boyd has seen better days since coach Anthony Seibold was forced to switch the underperforming fullback to pivot this year.

However, Johns believed the selection of new halves partner O'Sullivan for Friday night's NRL clash with South Sydney may change everything.

O'Sullivan has only played three NRL games since switching from the Sydney Roosters this year and a career total of just four.

But Johns believes the halfback may just be the key to a Boyd revival by finally bolstering a spine that he believes has let the Brisbane skipper down this year.

O'Sullivan finally gets his chance at No.7 after Jake Turpin copped a two week ban for a swinging arm on Penrith fullback Dylan Edwards last weekend.

"I think Boyd's best football is behind him but in his defence he hasn't really had a halfback - this is the first time," Johns told AAP.

"I love Jake Turpin but he is not a halfback.

"Friday night they have a proper halfback and I think that is going to help Darius - I am excited about it."

Boyd has appeared a shadow of his former self this year with Seibold forced to swap the former Test fullback with Brisbane five-eighth Anthony Milford this season.

Meanwhile, Seibold backed O'Sullivan to stand up to South Sydney with Brisbane's finals hopes on the line.

Seventh-placed Brisbane have lost just once in their last seven games ahead of their clash against a Rabbitohs line-up that has dropped out of the top four for the first time after three straight defeats.

"It is a big test for Sean. No doubt he will be targeted there, but he is a really good young player," he said.

Australian Associated Press