Mat Rogers has been performing admirably in the number 12 jersey but injured his ankle during the Wallabies' 37-15 win over Ireland last weekend, though he now looks likely to retain his spot at inside centre.
Giteau revealed the injury is not serious and he still hopes to make the squad for the New Zealand match, but was frustrated to have suffered another setback.
"I've got to go and have X-rays now on my thumb, but hopefully it's not too bad, but it's just frustrating," Giteau told the ABC.
"I broke my middle finger in a trial for the Brumbies and I was out for three or four weeks then, so hopefully it's nothing like that, just a dislocation, because I know people play with them all the time."
Giteau spent 35 minutes on the field for Queanbeyan and was happy with his performance, particularly with the knee that has sidelined him since May.
"The knee was fine, I was able to step and run, I felt I had a lot of confidence with my knee, I felt I could do everything that I need to do, so it felt good," he said.