World Cup-winning number eight Duane Vermeulen has joined the Springboks camp after injury, heaping further potential misery on the British and Irish Lions.

The 35-year-old powerhouse loose-forward appears ready to win his fitness race after ankle surgery, to be ready for Saturday's Lions Test series decider.

The 54-cap back-rower joined the Springboks camp in June only to suffer an ankle issue, and has been undergoing hyperbaric oxygen therapy in a bid to be fit to face the Lions.

Bulls head coach Jake White had cast doubt on Vermeulen's chances of taking on the Lions earlier this week, but the vastly-experienced forward linked back up with the Boks on Sunday.

"Duane will join us on Sunday and will be medically assessed as soon as possible," said Springboks head coach Jacques Nienaber.

"We will never risk a player who is not 100 per cent fit but he brings experience to the squad and it will be great to have him with us."

South Africa pummelled the Lions 27-9 in Saturday's second Test, to square the three-match series at one win apiece.

Makazole Mapimpi and Lukhanyo Am's tries helped the Boks seal a 21-0 second-half scoreline, with the Lions resoundingly beaten in Cape Town.

An ill-tempered affair saw Cheslin Kolbe prove fortunate to avoid a red card for tackling Conor Murray in the air, while the likes of Stuart Hogg, Maro Itoje and Faf De Klerk could yet come under citing officer scrutiny.

The Springboks have struggled in the back-row without talismanic Vermeulen, with Kwagga Smith battling to find his feet.

The hosts are also likely to be without Pieter-Steph Du Toit for next weekend's decisive Test, with the flanker having suffered a shoulder problem.

Sale Sharks lock Lood De Jager stood up manfully as a makeshift flanker off the bench in the second Test, shoring up the Boks' faltering lineout.

But Vermeulen's potential return will be the last obstacle the Lions will want to face, as Warren Gatland's men chase a first series win in South Africa since 1997.

"Experienced number eight Duane Vermeulen will join the Springbok team at their Cape Town base on Sunday after missing the opening two Tests against the British & Irish Lions due to an ankle injury," read a Boks statement.

"Vermeulen, who reported for duty briefly at the team's training camp in Bloemfontein in June, has been undergoing rehabilitation following surgery several weeks ago.

"However, his steady progress proved to be sufficient for Vermeulen to be called up to the squad that drew the Castle Lager Lions Series one-all with a convincing 27-9 victory on Saturday.

"Nienaber added that the Boks will know more about Pieter-Steph du Toit's injury on Monday."