Scotland co-captain Mike Blair was today ruled out of tomorrow's international with Australia.
The Edinburgh scrum-half failed a fitness test this morning on the ankle he injured in Saturday’s match against Fiji.
His place on the bench will be taken by Gloucester’s Rory Lawson, who is promoted from the A squad.
Blair had to be carried from the field after coming on to replace co-captain Chris Cusiter in Saturday’s 23-10 victory at Murrayfield.
He missed training on Monday and Tuesday and, although he did feature later in the week, has not recovered sufficiently.
The elevation of 15-time capped Lawson, 28, means Edinburgh’s Greig Laidlaw will start Scotland A’s match against Tonga at Netherdale tonight.
Glasgow’s Mark McMillan has been added to the Scotland A bench.