The Crusaders were handed a massive boost ahead of their Super 14 semi-final when lock Brad Thorn was cleared to start against the Bulls in Pretoria on Saturday night (AEST).

All Blacks workhorse Thorn has been in doubt all week with a tight hamstring that prevented him playing against the Blues in Auckland last week.

He emerged unscathed from training overnight and will take his place in the second row alongside Isaac Ross.

Thorn, who had been bracketed with Michael Paterson, will be a crucial presence in the Crusaders pack, marking hardened Springboks pair Victor Matfield and Bakkies Botha.

Halfback Andy Ellis, who has sore ribs, was listed as "likely to start" in a Crusaders media release on Friday but team management won't make a final decision until just before kick-off.

Kahn Fotuali'i is on standby to start, with Tyson Keats having arrived overnight from Christchurch as cover.

Head coach Todd Blackadder said the team had prepared well at their Johannesburg base and were excited about the challenge ahead. They will travel the short distance to Pretoria on the eve of the game.

Captain Richie McCaw said the team was aware of the importance of maintaining discipline against the Bulls.

"Playing at altitude, the ball flies much further and if you are up against a good kicker like (Bulls five-eighth) Morne Steyn, you can be punished anywhere inside your half," he said.

McCaw said the younger players would be told about the intimidating atmosphere at Loftus Versfeld but a good start from the Crusaders would hopefully subdue the expected 52,000 crowd.

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