Sundowns will host the La Liga giants at FNB Stadium (18h15 kick-off) on May 16 as part of the Nelson Mandela centenary celebrations.
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Downs had to get CAF's approval to reschedule their Champions League group stage match with Horoya from May 15 to May 22 to accommodate Barca's visit.
Sundowns president Patrice Motsepe said: "Mamelodi Sundowns and the Motsepe Foundation are honoured to play a humble role in the Nelson Mandela Centenary celebrations in honour of our icon Dr Nelson Mandela, who was respected and inspired people throughout the world.
"Dr Nelson Mandela often referred to the power of sports and football to unite people from different races and backgrounds."