The 23-year-old returned home following the game in Nelspruit and his club Glasgow have since confirmed he will undergo a period of physiotherapy prior to an operation, which is expected to keep him out of action for around nine months.
Warriors head coach Gregor Townsend said: "We're all gutted for Peter. He epitomizes everything that's good about the club, with his workrate and desire to improve. This earned him the Players' Player of the Season award last season and his first Scotland cap in South Africa.
"His reaction to such a serious injury on the field last week, showed how much he was willing to sacrifice himself for the good of the team, as he fought to get back up after his injury to be involved in Alex Dunbar's try."
Meanwhile, it is hoped that Warriors' hooker Pat MacArthur, who was injured during Scotland's defeat to Samoa, will be fit for the start of the new season. Scans have shown medial ligament damage meaning he'll be out of action for up to eight weeks. Back-row forward Ryan Wilson, who also had to leave the Scotland tour party early, is to undergo further tests on a shoulder injury picked up in the defeat to South Africa.