Sharks prop Lourens Adriaanse and lock Stephan Lewies have been called up to the Springbok squad in Port Elizabeth.
The Boks face Scotland at the NelsonMandela Bay Stadium in their final Test of the Incoming Series on Saturday.
Adriaanse replaces his provincial team-mate Tendai Mtawarira, who sustained an injury to his neck in last Saturday's 31-30 victory over Wales in Nelspruit.
Lewies comes into the squad for Flip van der Merwe, who injured knee ligaments late in the Welsh Test.
Both Mtawarira and Van der Merwe underwent scans in Port Elizabeth on Monday.
"Tendai has a bulging disc in his neck and he will consult with a specialist in Durban as soon as possible," said Springbok team doctor Craig Roberts.
"Flip hyper-extended his knee in a tackle and scans confirmed our clinical suspicions of a posterior cruciate injury. He will consult a knee specialist in Pretoria later on Tuesday."
Furthermore Willem Alberts, who can provide lock cover, left the field against Wales last Saturday after suffering a concussion and Bakkies Botha was released from the squad this week.
"We take concussion very seriously and have a set return-to-play protocol that Willem needs to progress through," added roberts.
"A final call on his availability will be made later in the week."
Springbok coach Heyneke Meyer said that Adriaanse and Lewies were the next players on the standby list.
"Lourens has been with us before and I'm sure he will slot back in easily," said Meyer of Adriaanse, who made his Test debut last November against France in Paris.
"Stephan was part of our training squad in Durban at the end of last month. He arrived in Port Elizabeth earlier today and looked good at our afternoon training session. He has been very good in Super Rugby this year and deserves this opportunity."
Adriaanse will join the Springbok squad in Port Elizabeth on Tuesday.