Two unnamed members of the England tour party in South Africa have returned “unconfirmed positive tests” for coronavirus.
The tourists were tested on Saturday after two members of staff from the hotel where they are staying tested positive.
Sunday’s rearranged opening one-day international in Paarl was called off 30 minutes before the 08:00 GMT start.
England players and staff are self-isolating in their hotel rooms.
The opening game of the three-match series on Friday was postponed after a South Africa player tested positive for coronavirus.
The South Africa squad were tested again on Friday evening and all returned negative results.
A decision on the final two matches of the series – due to take place in Cape Town on Monday and Wednesday – will be made once the England test results have been ratified by independent medical experts. That is unlikely to come before Monday.
It is possible that the games could be played on Tuesday and Wednesday. England fly home on Thursday.
England director of men’s cricket Ashley Giles said “the welfare of the players and support staff is our primary concern” and that the series opener “should not take place” while they await the results of further tests.
South Africa director of cricket Graeme Smith said: “We are deeply regretful of the situation we find ourselves in after the amount of time and energy that has been put in place to host a successful tour.”
The series is being played in a bio-secure ‘bubble’, with players only leaving their Cape Town hotel to play and train.
Before the Twenty20 series last month – which England won 3-0 – two South Africa players tested positive for coronavirus and two others were placed in isolation.
This series is England’s first overseas since their trip to Sri Lanka was abandoned in March following the outbreak of the pandemic.
After a delayed start to the home summer, England fulfilled all their planned matches, playing matches in a bio-secure environment and without fans in grounds.
Fast bowler Jofra Archer was forced to miss the second Test against West Indies after returning home between Tests, but no fixtures were affected.
‘Pretty much impossible’ for series to continue – analysis
BBC cricket correspondent Jonathan Agnew on BBC Radio 5 Live: “It is now really very serious.
“Members of the touring party doesn’t necessarily mean players – it could mean any of the coaching staff or backroom staff.
“It depends who the people are and how much contact they’ve had with everybody else, but you can imagine if you are in a bio-secure bubble then you’re all living quite closely together.
“If there is Covid-19 in the England camp now, what do they do?
“A serious issue is the question of quarantine should these two tests be confirmed. England are due to return on a chartered flight on Thursday but if there’s been contact between these two members of the touring party and the rest even their return home could be fraught with logistical difficulties.”
Former England captain Alastair Cook: “I would be very surprised in this series continued – that’s pretty much impossible.
“This is what unfortunately sometimes England captains have to deal with – Eoin Morgan will be in meeting after meeting.
“It was amazing this summer that nothing happened and, amazingly, every game happened.
“The ECB (England and Wales Cricket Board) have to get a lot of credit for organising it in that way. At times you probably thought the measures were a bit OTT, but they were all worth it to get all the games on.”
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