South Africa will be without three key players for their World Cup defence in September.

Fly-half Handre Pollard and centre Lukhanyo Am have been ruled out by respective calf and knee problems, while lock Lood de Jager is struggling with a chest problem.

Pollard's continuing injury issues mean the inexperienced Manie Libbok will be the Springboks' chief playmaker in the 33-man squad which was announced on Tuesday.

Siya Kolisi is expected to return from significant knee damage in a fortnight, enabling him to resume as skipper.

Pollard, Am and de Jager are among nine names on South Africa's stand-by list in the hope they will recover in time to play a role later in the tournament should other injuries hit the squad.

"This was one of the hardest selections we have ever had to make," said Springboks head coach Jacques Nienaber.

"Any of the 42-man training squad would do a great job, but injuries have played a part in the final selection and time unfortunately ran out for some real champions.

"However, we said from the outset that we wanted to name the best 33 players for the World Cup, and after giving 38 players a run in the last four Tests we are pleased with the make-up of the group, and we know we have proper depth in each position.

"We've picked a squad with a bunch of the players who can also cover alternative positions, which we'll need in a very tough World Cup.

"We were in a great position this year to have so many players knocking on the door for selection, but unfortunately, we could only select 33. Injuries have had a hand in the final selection, but they are part of the game, and we are excited about the quality of the players who can step in and perform at World Cup level – as many of the players who featured against Argentina showed last weekend."

Nienaber also announced that nine players would be placed on standby – five of whom will travel with the team to Cardiff and London for their last two World Cup warm-up matches against Wales (August 19) and New Zealand (August 25).

The nine players are Am (centre), Joseph Dweba (hooker), De Jager (lock), Jean-Luc du Preez (utility forward), Thomas du Toit (prop), Herschel Jantjies (scrum-half), Pollard (fly-half), Evan Roos (number eight) and Gerhard Steenekamp (prop). The five travelling to the UK on Saturday are Dweba, Du Toit, Du Preez, Pollard and Am.