The Crusaders' medical staff will work overtime ahead of Saturday night's (AEST) Super 14 rugby semi-final against the Bulls in Pretoria after lock Brad Thorn and half-back Andy Ellis were both struggling on Thursday.

The defending champions will sweat on Thorn's tight hamstring and Ellis's niggling hip injury, with the All Blacks pair key figures if the top-qualifying Bulls are to be toppled at Loftus Versfeld.

Thorn has been bracketed with Michael Paterson, who started in last week's 15-13 defeat of the Blues in Auckland, which earned the Crusaders an eighth successive appearance in the playoffs.

Ellis suffered a recurrence of an injury that has dogged him all year at training on Wednesday and has been bracketed with Kahn Fotuali'i.

Third-choice halfback Tyson Keats was to fly to Pretoria from Christchurch as cover.

The rest of the Crusaders starting 15 named are unchanged from the grinding Eden Park win, although there are changes on the reserve bench.

All Blacks prop Ben Franks and utility back Colin Slade both return from injury and fill the seats of Bronson Murray and Sean Maitland respectively.

Brought to you by AAP © 2024 AAP