Infotainment Factory: Cats to face daunting Blues challenge minus star back

Geelong is now the only undefeated side in the league after six rounds, and they'll have to face their next challenge without premiership defender Tom Stewart.

Stewart was ruled out of the Cats 26-point win over Brisbane at the Gabba on Saturday night, after an unfortunate and accidental head knock with Lion Kai Lohmann in the second term.

The five-time All-Australian jumped to spoil Lohmann's ball, but clashed his jaw with the back of his opposition's head, with the force pushing him backward and he landed flat on his back.

AS IT HAPPENED: Saturday NRL action

He looked in agony as he was attended to by club doctors, who quickly rushed him off to undergo his HIA.

Failing that, Stewart was subsequently ruled out with concussion, meaning he'll now be forced to sit out the Cats blockbuster clash with Carlton in round seven.

Cats two-time premiership coach Chris Scott said his side knew straight away that they'd be without Stewart in the second half, a brutal blow considering the heavy and wet conditions.

"It was really clear after halftime that he wasn't coming back on, so we moved on (with our structure)," Scott said post-match.

"I find it really difficult to convey the situation around this stuff (concussion).

"We'd be really clear if ... there's a concern there, but there's not.

"But my opinion on how he's looking shouldn't be valued much at all."

Now, the Cats must face up against Carlton's twin towers in Harry McKay and Charlie Curnow, who shared six goals between them in their 19-point takedown of the previously undefeated Giants in round six.

Scott says thoughts around how they'll structure up have already begun.

"Some thought will be required. There's no one we can replace that will be at Tom Stewart's level," he said.

"But we've been really clear for a long time that we think the best team will have to use a big squad. Depth is really important.

"This (Stewart out) tests us a little bit in terms of depth."

The Cats depth stood up to last year's grand finalists away from home, with youngster Ollie Dempsey thrown back alongside power forward Jeremy Cameron.

Geelong managed to restrict the Lions to just one goal after halftime, which was scored early in the third term.

Ollie Dempsey moved down back after Stewart was ruled out.

Zach Guthrie, Jack Henry, Jake Kolodjashnij and Sam De Koning held their own, with another challenge against Carlton's quick forwards lying ahead.

"Carlton's forward line forces you to think ... about how you set up. But it's a great opportunity for our younger key backs," Scott said.

"Stewart wouldn't have played on either of those guys (Curnow and McKay) anyway, but he does help."

Despite the obvious hole that will be left, Scott says his Cats will prepare accordingly in hopes of overcoming a fast-improving Carlton side, who sit 5-1 after six rounds.

"It's not insurmountable, we're up for the challenge," he said.

The Cats and Blues will face off on Saturday afternoon at Marvel Stadium.