Carlton coach Brett Ratten says the sky's the limit for young ruckman Robbie Warnock, and he might need to leap that high to counter West Coast's dynamic AFL ruck duo.

The 24-year-old impressed in the Blues' convincing elimination final win over Essendon.

But he will have to further lift his game in their sudden-death semi-final at Perth's Patersons Stadium on Saturday to counter towering veteran Dean Cox and the athletic Nic Naitanui.

The coach was delighted by Warnock's progress this season, his third at the club after a slow start to his career at Fremantle.

"Big men in finals, their reputations really grow when they stand up and we spoke to Robbie about that leading into the (Bombers) game," Ratten said,

"I thought he responded outstandingly.

"It wasn't just about how he applied himself, (but also about) how he followed up and his tackling, we were really pleased."

Ratten said there was room for the 24-year-old's marking to improve but he had a big future.

"I think if he believes as much as we believe in him, the sky's the limit."

The pressure on Warnock is set to further increase with Blues ruck-forward Matthew Kreuzer rated almost no chance of playing as he battles a mystery foot complaint.

Ratten said tests had so far failed to uncover what was causing numbness in Kreuzer's foot, which has left him sidelined since their round-24 loss to St Kilda.

"We thought we were on top of it but we can't identify exactly what it is."

Utility Bryce Gibbs is also only a "slim chance" of making the Blues' flight to Perth on Thursday afternoon.

"The big one for us is if he gets a knock or something like that," Ratten said.

"We have to take that into consideration, that he'd be out for the game and the risk of that happening and what it does for the other 21 men, it's pretty unfair."

Ratten believed picking the best line-up to face the Eagles was a tough proposition.

"It's always a concern, if you take a running team and a smaller team, if you get an injury to a tall it really leaves you short."

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