Geoff Cross became the second Scotland front row forward forced to return home from South Africa because of injury, team officials said on Monday.
The prop came on as a replacement in the 27-17 loss to Samoa on Saturday in the opening round of a four-nation tournament also featuring the Springboks and Italy.
But a shoulder injury has ruled him out of the Test against South Africa this Saturday at Mbombela Stadium in Nelspruit, which will be staging Test rugby for the first time.
Hooker Pat MacArthur, whose Test debut lasted just five minutes against the Pacific islanders before hobbling off at Kings Park in Durban, withdrew from the tour on Sunday with a knee injury.
Others battling against the clock to recover from injuries include flank and captain Kelly Brown, and officials said the planned Tuesday team announcement has been delayed.