Duane Vermeulen, attempting a miraculous Test comeback from an ankle injury, trained with the Springboks on Monday assistant coach Deon Davids said.
The back-row forward underwent surgery two months ago after being hurt in a domestic match and was written off as a possible starter in the three-Test series against the British and Irish Lions.
But the number eight joined the camp on Sunday amid speculation as to what role he may play in the series-deciding third Test against the tourists in Cape Town on Saturday.
With flanker and 2019 World Rugby Player of the Year Pieter-Steph du Toit nursing a shoulder injury, there have been suggestions that Vermeulen could start, or be on the bench.
If the third Test has come too soon for Vermeulen and he could be deployed to offer guidance and assistance with training and analysis.
Head coach Jacques Nienaber has ruled out selecting the 2019 Rugby World Cup winner if there is the slightest doubt about his fitness.
"We will never risk a player who is not 100 percent fit, but he brings experience to the squad and it will be great to have him with us," he said.
Before flying from his Pretoria home to Cape Town at the weekend, Vermeulen underwent weeks of intense rehabilitation at his franchise, the Bulls.
Davids said the presence of Vermeulen, who turned 35 last month, had an immediate positive impact on the camp.
"It is really fantastic to have Duane back with the group and he joined our training session today," he told an online news conference.
"He has already been part of our review sessions. We will hopefully have more details about his injury tomorrow."
Another concern for the world champions is scrum-half Faf de Klerk, who went off with a hamstring injury during the second half of a 27-9 triumph last Saturday.
Were De Klerk ruled out, Herschel Jantjies would be the obvious replacement with third-choice Cobus Reinach promoted to the bench.
Meanwhile, Nienaber has added winger Rosko Specman, scrum-half Jaden Hendrikse, hooker Johan Grobbelaar and loose forward Dan du Preez to the squad.
Specman and Du Preez were released recently when the squad was trimmed while Hendrikse and Grobbelaar have been called up for the first time.
"We have a tough Rugby Championship series after the Lions and, given the strict Covid-19 protocols we adhere to, decided to bring the players in sooner rather than later," said Nienaber.
South Africa start their campaign in the Southern hemisphere Rugby Championship against Argentina on August 14.