The British and Irish Lions will meet the Sharks for a second time in four days after the Bulls were prevented from playing at Loftus Versfeld on Saturday because of an outbreak of coronavirus.
The Lions won the first fixture 54-7 in an eight-try romp at Emirates Airline Park on Wednesday night, but the Sharks have been identified as the only team able to step in at short notice.
"The choice of the Sharks was dictated by the fact that they have been in a bubble, have returned negative tests throughout and were prepared to take on the fixture," SA Rugby chief executive Jurie Roux said.
"No other team in the country could meet those conditions right now – without going into a five-day lockdown. It is not an ideal situation, but Covid has made sure that we do not live in an ideal world."
The Lions have released no further details of the Covid status of their squad after nine players and five members of staff were forced to self-isolate at the team hotel on Wednesday.
A player and one of Warren Gatland's management team produced positive tests, forcing an additional 12 personnel into quarantine. The Sharks fixture is subject to the Lions being able to field a team.
"We're very grateful to the Sharks for agreeing to play us again this Saturday at Loftus Versfeld," Lions managing director Ben Calveley said.
"We have further Covid testing scheduled for today (Thursday) and tomorrow. The results of those tests will determine whether we will be able fulfil this fixture, but, as it stands, we are optimistic.
"We remain committed to the tour in South Africa and determined to rise to the challenges created by the Covid pandemic."
Gatland revealed that one of the two coronavirus cases confirmed by Wednesday's round of PCR testing is a "very weak positive" and that another test could produce a negative.
If that is the case, then a number of personnel will be given the all-clear to rejoin the touring party.
The Lions must also assess the fitness of their players. Wales wing Josh Adams has started three successive matches while the enforced eight changes made to the 23 for the first game against the Sharks have torn up selection plans for Saturday.
"My understanding is that one of the positives is a very weak positive and if he is retested and it's negative then his close contacts should be OK," Gatland said.
"Then I'll need a report back from the medical team about how the players are after the Sharks game.
"Someone like Josh Adams has fronted up three games in a row, so he's a player we probably need to rest.
"I have to take my hat off to these players, they've really dug deep for the whole squad. It just shows to me what it means to play for the Lions."
