The mystery surrounding Simon Black's calf injury is no closer to being solved with Brisbane Lions coach Michael Voss claiming he is "not sure" when the Brownlow Medallist will return to the field.

And Voss offered no guarantees to key players Mitch Clark and Ash McGrath ahead of the undefeated Lions' AFL clash with big improvers Melbourne on Saturday night, despite both completing their suspension.

Black was named for the Lions' last round clash with the Western Bulldogs but succumbed to the calf complaint and pulled out hours before the first bounce.

Despite the huge loss, the Lions surged to a 22-point win over the highly touted Dogs to maintain their unbeaten start to the season.

Voss seemed at a loss as to when Black would return.

"At this early stage I am not sure to be honest," he said on Monday.

"Scans have not shown muscle damage ...(but) the fluid has now got in his calf and it's hanging around, so it seems to be affecting the dynamics.

"At this stage we're certainly not going to risk it. We'll be more on the conservative side.

"We want him fit and healthy, and we'll make sure that he's fit and healthy before we put him out there."

The Lions have won the opening four games of the season for the first time since 2002 - a premiership year for the team.

And Voss claimed he was leaning toward the "if it ain't broke, don't fix it" theory against the improving Demons.

Asked if Clark and McGrath were automatic selections, Voss said: "It's not as automatic as it may seem.

"I think all of the players that played on the weekend did enough to be able to warrant their spot back, and then it comes down to what you need.

"It could be the fact that we feel like the 22 did such a great job that they deserve another go."

But it would be hard to see Voss leaving out Clark - particularly with the influential ruckman being booked in for a Thursday press conference ahead of his 50th AFL game.

While the Lions are one of only two unbeaten AFL teams, Voss said the Lions still had plenty to prove - starting with the resurgent Demons.

"The players are reasonably confident and they have belief that we can compete against most sides - whether that makes us elite or not, I don't think we've proven that," he said.

"Geelong are elite, we hope to be.

"We have beaten a side (Dogs) that has quite rightly been touted as a top four contender - to come through that was pleasing.

"(But) the three sides we have coming up - Melbourne, Sydney and Freo (Fremantle) - are all in really good form.

"It's going to be a nice challenge."

Saturday night's game marks the Lions' sole regular season match at the MCG.

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