New Zealander Dylan Hartley will captain England in the third test against South Africa in Port Elizabeth after Chris Robshaw was ruled out with a cracked bone in his right thumb.

Robshaw suffered the injury in the first test but it was only revealed in a scan after he took another knock at the weekend.

"I'm absolutely gutted," he said in a statement. "I've been very proud and honoured to lead this group during the Six Nations and on this tour and it's a difficult way to end the season."

Coach Stuart Lancaster said medical advice was that Robshaw should not play.

"Dylan Hartley will captain the side. He has been a key part of our leadership group and I know he will step up to the task on Saturday.

"Dylan has always been part of the leadership group, he's driven training, he's the first-choice in his position and is respected by the players."

South Africa clinched the three-test series after defeating England 36-27 at Ellis Park in Johannesburg in the second match.

England will also be without scrumhalf Ben Youngs due to a shoulder injury.

Meanwhile, uncapped fullback Joe Pietersen has been added to the Springbok squad ahead of the third test.

The 28-year-old Pietersen, who plies his trade with South African Super Rugby franchise the Stormers, has been added to the squad as cover for Patrick Lambie, who suffered an ankle injury in the second test.

The hosts, who hold an unassailable 2-0 lead in the three-test series, are already without Zane Kirchner, who played fullback in the first test before being ruled out of the series with a knee injury, while centre Frans Steyn will miss the third test as he will be getting married.

Fullback Lambie and flank Willem Alberts, who injured knee ligaments in the second test, have not been ruled out of Saturday's third test and a final decision on their availability will be made on Wednesday.

"Joe has always been part of our plans and also attended our final planning camp in Durban shortly before the England series started," Springbok coach Heyneke Meyer said in a statement.

"Injuries are part of the game and something you can't plan for, but we always knew Frans was not going to be available for this test. Joe knows our systems and game plans and I'm sure he will slot in easily."

- Reuters