Adam Hastings, the stand-off, and Huw Jones, who can play centre or full-back, will both miss the trip to Chile and Argentina after sustaining injuries on club duty.
Hastings injured his hamstring and Jones his back in the final round of Premiership games this season.
Despite losing two backs to injury Scotland have not called up like for like replacements but they have announced that Glasgow Warriors hooker Johnny Matthews has joined the squad. The uncapped Matthews was Glasgow’s top try-scorer this season.
The games against Argentina will take place in Jujuy on July 2, Salta on July 9 and Santiago Del Estero on July 16.