Grimes has an inflamed tendon in his left knee which had not settled following Scotland's game against the Barbarians last week and forced him to cut short his training session yesterday. He has been referred to a specialist for further consultation. His place has been taken by his club colleague.
Craig Hamilton's promotion means Edinburgh Rugby's Alastair Kellock is brought into the squad. The formers Allan Glen's player is drafted on to the bench.
Craig said today: "I owed my chance to win my first cap out in Australia to Stuart Grimes, because he was suspended and his injury now is giving me another chance.
"I feel for him because he's such a great player. I've played alongside him at Newcastle for a few years now and he's always giving me advice and tips to become a better player."
Meanwhile Edinburgh Rugby scrum half Mike Blair took full part in training today and remains in the starting line-up for Sunday's Test.