De Kock refused to play in Tuesday's victory over West Indies after an order from Cricket South Africa that all its players should take a knee before games at the World Cup.
De Kock declined to do that and made himself unavailable, but issued an apology and explanation two days later. He said he felt his rights were taken away by forcing him to make the gesture and that he would take a knee in the future.
He removed his cap and took a knee Saturday alongside all the other players on the field in Sharjah.
South Africa captain Temba Bavuma won the toss and chose to field. De Kock replacing Heinrich Klaasen was the only change to the team that beat the West Indies by eight wickets.
Sri Lanka selected the same team that lost to Australia by seven wickets on Thursday.
South Africa and Sri Lanka have one win and one loss in the Super 12 stage and are chasing Group 1 leaders England and Australia. The top two teams will reach the semifinals.
South Africa: Temba Bavuma (captain), Quinton de Kock, Reeza Hendricks, Aiden Markram, Rassie van der Dussen, David Miller, Dwaine Pretorius, Kagiso Rabada, Keshav Maharaj, Anrich Nortje, Tabraiz Shamsi.
Sri Lanka: Pathum Nissanka, Kusal Perera, Charith Asalanka, Avishka Fernando, Bhanuka Rajapaksa, Dasun Shanaka (captain), Chamika Karunaratne, Wanindu Hasaranga, Dushmantha Chameera, Maheesh Theekshana, Lahiru Kumara.
More AP sports: https://apnews.com/hub/apf-sports and https://twitter.com/AP—Sports