The British and Irish Lions' match against South African provincial team Vodacom Bulls on Saturday has been postponed because of Covid-19 cases in the hosts' camp.
It is the first tour game to be affected in a country that is experiencing a surge in infections.
Tour organisers hope to reschedule the game or find different opponents for the Lions.
Doubts also exist over South Africa's warm-up against Georgia on Friday.
The Springboks are isolating, with training suspended as they deal with an outbreak.
South African rugby bosses said: "Four Bulls players and one member of management returned positive tests which, in combination with their close contacts, made it impossible for them to field a team, according to series safety protocols.
"Series regulations make provision for additional midweek matches to be added on agreement between the organizations.
"Meanwhile, four positive results among the Georgian team and four additional positive tests among Springbok players (Marvin Orie, Frans Steyn, Handre Pollard and Frans Malherbe) plus six among management, including head coach Jacques Nienaber, and one masseuse, have further complicated planning."
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SA Rugby chief executive Jurie Roux said: "These positive results are a setback and have underlined the danger of transmissibility of the Delta variant.
"The Springboks' second Test against Georgia is now in serious doubt."
A decision on Friday's game will be made on Wednesday,
"The priority is to maintain the integrity of the Test series and we will continue to focus on that," said Roux.
The host nation previously suspended training on 27 June because of three positive tests, but were later cleared to play.
Second row Lood de Jager earlier tested positive, with Vincent Koch, Herschel Jantjies and Sbu Nkosi having returned positive results on 27 June.
Jantjies later returned a negative test and was a replacement when the Springboks beat Georgia 40-9 last Friday in Pretoria - their first Test match since winning the 2019 World Cup.
The following day the Lions played their first game on South Africa soil, beating the Sigma Lions 56-14 in Johannesburg.
South Africa is battling a third wave of coronavirus and entered a strict lockdown just as the Lions arrived last week.
Speaking before the game was called off, Lions defence coach Steve Tandy said the tourists would adapt to any disruption.
The Lions game against Cell C Sharks on Wednesday, 7 July will go ahead.
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