Prop McCallum is called up as cover after fellow Edinburgh tighthead WP Nel suffered a calf strain on Saturday. Nel remains with the squad as he attempts to get fit for Saturday’s match against Ireland, which is also at Murrayfield.
Glasgow Warriors hooker Brown has full recovered from injury and returned to the squad in place of club mate Grant Stewart, who has been released back to his club, the Scotland Rugby Union said on Monday.
Flanker Sam Skinner, who went off with an ankle injury early in Saturday's game, has gone back to Exeter Chiefs for further assessment. He is a doubt for the rest of the competition.