An Achilles tendon injury to full-back Khuliso Mudau spoilt a 2-0 victory by Mamelodi Sundowns over Marumo Gallants on Wednesday in the South African Premiership.
Mudau was part of the South African team that made history at the 2026 World Cup by reaching the knockout stage for the first time.
"It is a serious injury and a big loss not only to us, but also South Africa," Sundowns' Portuguese coach Miguel Cardoso told reporters.
South Africa begin their 2027 Africa Cup of Nations qualifying campaign in September by hosting Guinea and visiting Eritrea.
Mudau left the pitch at Loftus Versfeld stadium in Pretoria on a stretcher late in the first half with Sundowns one goal ahead.
Sundowns took the lead on 21 minutes when a cross fell to Malibongwe Khoza, and the defender slammed the ball into the net from close range.
Marumo were outplayed but survived falling further behind until the 67th minute when Cassius Mailula struck a rising shot over Cameroonian goalkeeper Merlin Lako.
Sundowns climbed from seventh to third, level on seven points from three matches with leaders Orlando Pirates and second-placed Kaizer Chiefs, but behind on goal difference.
Marumo, who narrowly avoided relegation last season, dropped two places to the bottom of the table.
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