Scotland lock Richie Gray is in a race against time to be fit for Sunday's Test against New Zealand at Murrayfield.
Gray has been battling to overcome an ankle injury of late and was withdrawn from the Sale Sharks side which beat London Irish last weekend.
The 23-year-old missed Monday's training session and the Scottish Rugby Union confirmed that he "undertook an individual programme with the squad's medical team, following on from his ankle rehabilitation work over the last week."
New captain Kelly Brown also missed training because he played for Saracens against Wasps on Sunday, while Glasgow Warriors prop Gordon Reid trained with the national team due to numerous front-row troubles.
Scotland team manager Gavin Scott explained Reid's involvement with the squad.
"We've asked Gordon to train with us today as Kyle Traynor played for his club, Bristol, yesterday and will thus follow our usual protocol and not be training with the squad today," he said.
Coach Andy Robinson will name his team on Tuesday, and if Gray is sidelined it means there will be at least five changes from the side which beat Samoa in their last Test in June.
Centre Joe Ansbro and scrum-half Chris Cusiter are unavailable due to injury while number eight Richie Vernon did not make the initial squad and tighthead prop Euan Murray is not available due to religous reasons as the match falls on a Sunday.