Kolisi had major knee surgery in April but South Africa are confident he will be fit in time for their first pool game against Scotland in Marseille on September. 10.
There are 12 newcomers but the Boks have kept the bulk of the side that won the World Cup in Japan four years ago.
But Am, who twisted his knee in a warm-up test against Argentina on Saturday, and Pollard, who has a long-running calf injury, were among the notable omissions when the squad was unveiled at an elaborate televised ceremony on Tuesday.Â
Also out is Lood de Jager, the giant lock who was also part of team four years ago. He has an unspecific chest complaint, SA Rugby said.
"There were some tough decision that had to be made," coach Jacques Nienaber said.
Am, De Jager and Pollard have been placed on standby with six other players and Nienaber said he was hopeful they may return to full training before the start of the tournament and be available in the event of injury to others.
Kolisi is expected to play in one of the two warm-up internationals that the Boks will play over the next fortnight, against Wales in Cardiff on August 19 and New Zealand at Twickenham on August 25, as he looks to prove his fitness.
South Africa play in Pool B at the World Cup where they also meet Romania, Ireland and Tonga.
SOUTH AFRICA RUGBY WORLD CUP SQUAD
Backs: Damian de Allende, Kurt-Lee Arendse, Faf de Klerk, Andre Esterhuizen, Jaden Hendrikse, Cheslin Kolbe, Jesse Kriel, Willie le Roux, Manie Libbok, Makazole Mapimpi, Canan Moodie, Cobus Reinach, Damian Willemse, Grant Williams.
Forwards: Pieter-Steph du Toit, Eben Etzebeth, Deon Fourie, Steven Kitshoff, Jean Kleyn, Vincent Koch, Siya Kolisi, Frans Malherbe, Malcolm Marx , Bongi Mbonambi, Franco Mostert, Ox Nche, Trevor Nyakane, Marvin Orie, Kwagga Smith, RG Snyman, Marco van Staden, Duane Vermeulen, Jasper Wiese .
