Giteau was a major doubt for the series opener after sustaining a dislocated finger in a club match for Canberra side Queanbeyan.
The 24-year-old, who made his international debut in 2002, was using the match to build up his match fitness after suffering a knee problem playing for the ACT Brumbies in the Super 14 back in May.
But Giteau now looks set to start on the bench after winger Rathbone was ruled out of the weekend's game with a torn hamstring.
Wallabies coach John Connolly said: "Clyde has progressed quite well since injuring his hamstring but is still a little bit off running at full pace.
"It is not a serious problem but we thought it best to give him the extra week to get it right."
Back-rower Wycliff Palu will also miss the match in Christchurch with a hamstring injury with Western Force's Scott Fava tipped to deputise and make his international debut.
Fava, 30, was named in the Wallabies' 22-man squad for last year's tour of Europe but is still waiting yet to make his international bow.
Connolly added: "Cliffy's got a small tear in his hamstring which is not a serious one but we didn't want to risk doing further damage by playing him this weekend.
"We've been happy with the way Fava has trained throughout the campaign and he deserves his opportunity on the bench."
Queensland back-rower John Roe has come into the Wallabies squad as a replacement and Connolly is set to name his side on Tuesday before the players jet out to Christchurch on Wednesday.