Alaalatoa was in the side to face Ireland at Suncorp Stadium in Brisbane Saturday, however, the Brumbies prop succumbed to a knock to his ankle sustained during training Thursday.
Australia have now added Robertson to the bench in response to the 24-year-old's injury, it was announced Friday.
Waratahs prop Robertson has not featured for the Wallabies since last year's clash with England at Twickenham in November.
