Prop Moray Low has been forced out of Scotland's squad for the two-Test trip to Argentina next month.
The uncapped 23-year-old has been told it will take at least six weeks to recover from the ankle injury he sustained in Glasgow’s Magners League win against Munster on Saturday.
Edinburgh’s 25-cap prop Craig Smith, 29, has been promoted from the Scotland A squad to replace Low.
Head coach Frank Hadden has also called up Glasgow’s uncapped back Max Evans, 24, to join brother Thom in the Scotland squad.
Low had a fine season for Warriors and Hadden last week confirmed the prop had been among a group of players “chapping at the door” of the senior national team.
However when Scotland take to the field in Rosario on June 7 and Buenos Aires on June 14, Low will be continuing his recovery at home.
Scotland team doctor James Robson said: “Moray will be subject to further assessment but on reviewing the X-ray he will be in a compression boot for two weeks then undergo a period of rehabilitation of between four to six weeks, which will rule him out of the tour.”
Replacement Smith had been due to take part in the Churchill Cup but will instead provide back-up in the senior squad, with more players still to be added by Hadden.
With senior backs Nikki Walker and Rory Lamont failing to overcome leg and knee injuries in time to be selected, Hadden turned to Max Evans who has previously served the Scotland A and Sevens teams.
Hadden said: “We have decided to promote Max Evans from the Scotland A squad.
“Max has played well in the Magners League for Glasgow and is another to have benefited from involvement with both Scotland A and Scotland Sevens.
“We are still waiting to see if Simon Webster will recover from his hamstring injury to make the tour. He’ll be subject to further monitoring and we’d hope to make a decision on Simon next week.”