DANIEL Merrett's hamstring injury is worse than first thought, with no timeframe set on return for the Brisbane Lions fullback.

Merrett suffered the injury during a training session in the build-up to round two against North Melbourne and was initially expected to miss two or three weeks.

However, as the rehabilitation drags on, coach Justin Leppitsch confirmed on Thursday morning, the defender was no closer to returning to action.

Leppitsch said Merrett’s hamstring was now healed, but some blood was pooling around the nerve, which had slowed down the healing process.

"I have no idea," Leppitsch said, when questioned on Merrett's likely availability.

"Every week I hear it's another week or two, then it's another week or two and the same path has continued. It's not as obvious as most other injuries, this one.

"It's taking time unfortunately until that blood goes away.

"He's got a bit of a pinched nerve at the moment, that's the thing that's causing all the issues."

BUPA Recovery Report

In Merrett's absence, the Lions have gone with an extremely young and inexperienced backline that has still impressed in recent weeks.

Justin Clarke (21) has taken the opposition's best forward, while Harris Andrews (18), Darcy Gardiner (19) and occasionally Marco Paparone (20) have filled the other key posts.

Leppitsch said he was concerned the extra responsibility would take its toll at some stage.

"I'm concerned when you've got four or five kids in the one line, how long they can hold up for? That's an obvious concern," he said.

"Having Daniel back would definitely alleviate a lot of those issues because they can work around him.

"Justin Clarke is playing like a 100-game player at the moment, taking in all that pressure and doing such a good job.

"It's a bit unfair on the young fella. He's been thrown to the wolves to not only be the main man but to direct the young boys around and he's done a terrific job."

Leppitsch confirmed James Aish would retain his spot to play Essendon on Sunday, after the teenager's impressive 18-disposal performance against Port Adelaide following a stint in the reserves.