De Villiers has called up flanker Steven Sykes and lock Jean Deysel of the Sharks, Cheetahs prop Wian du Preez, Stormers centre Morgan Newman and Golden Lions half-backs Jano Vermaak and Earl Rose.
Rose was in the Springbok squad at the end of last year but did not feature in the Tests against three of the four Home Unions, while du Preez toured England and Wales at the end of 2007 but did not play. Vermaak was in the 2007 Emerging South Africa squad at the IRB Nations Cup and Newman featured for the Emerging side in 2007 and 2008.
With the Bulls having qualified for the semi-finals of the Super 14, the likes of Bakkies Botha, Bryan Habana, Victor Matfield and Pierre Spies are all missing from the 23-man squad.
First-choice fly-half Ruan Pienaar was not considered due to injury but de Villiers expects him to be fit in time for the first Test against the Lions on June 20.
"Ruan is expected to be out for about three weeks and we will closely monitor his progress," said de Villiers after Pienaar strained his ankle in the Sharks' narrow defeat to the Bulls last weekend.
"Then I will take it from there. If you look at how he played last Saturday and the games he took part in before that, all he needs is a bit of sharpness, but he is still one of the top fly-halves.
"I am hoping that he will be fit to play in the first Test against the Lions in Durban but we are fortunate in that we have adequate cover in the fly-half position if it is required".
Other players currently unavailable are centre Jaque Fourie, who is getting married next Saturday, and Francois Steyn and Deon Carstens, who are both injured.
Stormers skipper Jean de Villiers has been included, however, despite missing the end of the Super 14 season through injury.
The South Africa training squad will assemble in Pretoria on Monday and travel to Windhoek on Thursday, May 28.
The Springbok squad for the three-match Test Lions series will then be named on Monday, June 1, 19 days before the two sides square up in Durban.
South Africa training squad
Forwards: Ryan Kankowski, Juan Smith, Heinrich Brussow, Jean Deysel, Schalk Burger, Andries Bekker, Johan Muller, Steven Sykes, John Smit, Adriaan Strauss, Bismarck Du Plessis, Tendai Mtawarira, Wian Du Preez
Backs: Odwa Ndungane, Jongi Nokwe, JP Pietersen, Jean de Villiers, Adi Jacobs, Morgan Newman, Peter Grant, Earl Rose, Ricky Januarie, Jano Vermaak