Elliot's importance was heightened by the unavailability of Mahonri Schwalger, ruled out by a knee injury.
Rennie, who was yesterday running the rule over the Brumbies after their upset 26-23 win over the Bulls in Pretoria, said tighthead prop Ben Tameifuna would have covered hooker if Elliot had not played.
The language of Rennie and Crusaders coach Todd Blackadder after the match suggested they expected the Bulls to win at Loftus Versfeld. Instead it is the men from Canberra who stand between the Chiefs and a consecutive title.
Like the Sharks, the Chiefs' final rivals last year, the Brumbies face a tough travel schedule from the republic, but that shouldn't detract from the achievements of Rennie's men.
They were written off by many after the heavy loss to the Crusaders in Christchurch three weeks ago, but showed the necessary steel and inspiration - led by their defence and pack - to stand on the brink of a deserved second title.
Rennie said he was impressed by the Brumbies' performance at Loftus. But Jake White's men are unlikely to offer too many surprises.
"They play a certain style ... They don't play much footy down their own end, they go for the aerial assault, play territory and they strangle you through their set piece.
"They'll be well organised and will certainly come here with the belief that they can beat us. It should make for a hell of a fixture."