BRISBANE should lean all the way into a smaller forward line as it ponders how to replace Jack Gunston.

Gunston's knee injury, which will keep him sidelined until at least a qualifying final, if not beyond, raises a philosophical question for coach Chris Fagan – three tall forwards or two?

Since presenting Oscar McInerney with his debut early in 2017 to play as an understudy to Stefan Martin, Fagan has preferred three whenever he's had a chance.

That should change.

The Lions have been a low-possession team, prepared to kick quickly from stoppages and give their taller players opportunities ahead of the ball. They want the extra 'tall' to either mark it or force another stoppage – the phase of the game they are so strong at.

This year it's been Joe Daniher, Eric Hipwood and Gunston, with the three-time premiership Hawk taking the place of new Magpie Dan McStay.

Although Gunston and McStay have significant differences in the way they play, for all intents it kept the three-tall model in place for Fagan.

Instead of McStay being the player to run up to the wing and provide a target for the Lions as they exited their defensive 50, that role has now been shared between Daniher and Hipwood.

And while injury has forced its hand, Brisbane now has a chance to explore a dynamic set-up that could help take it to the final Saturday in September.

Does it stay put with the current structure and recall Darcy Fort as a specialist forward or inject speed by retaining Deven Robertson in the 22 or recalling youngster Kai Lohmann?

Fagan had a look at both models during Gunston's three-match absence following the mid-season bye, with mixed results.

Fort played as a forward against Sydney in round 14, while Lohmann came in against St Kilda the following week and Cal Ah Chee for Lohmann against Richmond the week after that.

Brisbane won all three matches.

Fort offers the safety of a strong contest on long down-the-line kicks, which has occasionally been a question mark for Brisbane (refer to the final 10 minutes in the recent loss to Melbourne).

However, arguably its best performance of the season came against the Tigers, with a set-up that featured Cam Rayner as the pseudo third tall and surrounding him with Charlie Cameron, Linc McCarthy, Zac Bailey and Ah Chee.

While Daniher cashed in with five goals that night, McCarthy (three), Cameron (two) and Bailey (two) all profited in the 20-goal output.

The week before against the Saints it was the bigs that did the job with Hipwood and Daniher combining for six goals against Ross Lyon's stingy defence.

Former skipper Dayne Zorko is also back now and in that mix to create havoc.

Not only do they have a potent attacking combination – as seen in the third quarter of Saturday's win over Adelaide – more importantly they're a defensive menace when the mindset is right.

Team defence has been the biggest improvement in Brisbane's game this season, and it's the element that will get the greatest test against Collingwood on Friday night.

Extra speed in the front half can only help that.

Daniher is having an All-Australian calibre season and Hipwood has been a regular contributor. Back those two to do their jobs when the ball is in the air and the ground level players will do the rest.

Gunston's injury is a blow for both the man himself and the team, but it could prove to be a silver lining if the Lions are bold.