England have expressed concerns over the integrity of the teams' bio-secure bubble in South Africa, leaving the ODI leg of their tour in jeopardy, after a positive test for Covid-19 from the hosts' camp led to the first ODI being postponed on Friday.

The match was called off an hour before the toss and has been rescheduled to Monday, with all players and hotel staff to be retested on Friday evening.

However, South Africa have yet to determine how one of their players contracted the coronavirus and, although they maintain their confidence that the bio-secure environment works, a further round of tests scheduled for Friday afternoon may decide whether the three matches are able to go ahead.

"There is a cause for concern and England has expressed a concern. England are questioning the confidence they have in the bio-secure environment and rightfully so," Dr Shuaib Manjra, CSA's chief medical officer, said.

"If there has been a player who tested positive in the last week, they have cause for concern and we respect that concern. We met with the English medical team and we have planned out a way. We will retest all players and hotel staff [tomorrow, later brought forward]. We will await the results and determine a course of action and then on Tuesday before the final ODI we will retest the team again."

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South Africa's players have so far been tested five times, three times before the start of the T20I series which revealed two positive cases, and once in between the T20Is and ODIs. Although CSA have declined to confirm the names due to doctor-patient confidentiality, David Miller and Andile Phehlukwayo are widely understood to be the first two players in question.

The first player who tested positive did not enter the bio-bubble and isolated on his own while the second was removed from the bubble when he tested positive two days later. Both players tested negative on the fourth round of tests, just before the start of the T20 series last Friday, and rejoined the squad last Saturday.

The third positive case was discovered a week later, from a test before the start of the ODIs yesterday, and CSA is unsure how it came about. Heinrich Klaasen was a notable absentee from Tuesday's final T20I, with his captain Quinton de Kock stating at the toss that he was sick.

"This test surprised us because we have confidence in the integrity of the bio-secure environment," Manjra said. "Further tests indicate that this is a more recent case that occurred within the bio-secure environment. So clearly there seems to be some kind of breach which we have investigated in great detail to try and determined where this happened.

"We have traversed a couple of different spaces, trying to recount some of the events: speaking to the player, looking at security cameras, looking at other information and we haven't been able to date to identify where the source was but clearly it's cause for concern."

The situation is understood to have unsettled the England camp, who have been staying at the same Vineyard hotel as the South Africa squad, albeit in separate wings with mixing between the two squads banned. Communal areas have been used on a rota basis and deep-cleaned between whiles, with the hotel staff also staying on the premises. Outside of travel to matches and practice, the teams' only other authorised departures from the hotel grounds have been for rounds of golf at Boshenmeer, near Paarl, again subject to strict protocols.

England's 24 players, plus support staff, are due to leave South Africa on a chartered flight on December 10. With the prospect of Christmas at home for some members of the squad, and imminent stints in Australia at the Big Bash for others, there is believed to be a reluctance among the players to jeopardise those plans.

A scheduled joint press conference between ECB and CSA was cancelled soon after the match had been called off, with Ashley Giles, the team director, later addressing the situation in a statement.

"On behalf of the England touring party and the ECB, I would like to thank Cricket South Africa for their collaborative approach to postponing today's one-day international," Giles said.

"Our number one priority is the health and safety of the England team and management group, and the correct decision was made following discussions between the two boards and respective medical teams.

"The England party will remain at its base in Cape Town on Friday and Saturday, and we are hopeful that the three-match series will be played before we depart next Thursday starting with the match at Paarl on Sunday."

In conceding that a player may have breached protocols, Manjra was adamant that no-one was allowed to leave the team hotel in Cape Town unsupervised.

"I can categorically state that there is no player who is able to leave the hotel environment by virtue of the fact that there is security around and the security will not allow the player to leave, unless that player is leaving in an assigned vehicle which is an official vehicle with an official driver," Manjra said.

"There is a command centre here led by the Colonel from the Claremont Police Force and they strictly enforce the bio-bubble. They wouldn't allow anybody to leave."

However, earlier on in the tour, players did leave for what appear valid reasons. "In fact some players left as a group to go across to the Oval [across the road from the hotel] to train and that became a matter of concern because they had seen it and we had addressed that concern with the Colonel and the command centre. It is impossible for any player or official to leave this."

That revelation gives credence to Manjra's suggestion that the bubble is not working as intended. "I am fairly convinced that 99% of the time this environment is working," he said. "There may be a breach that is unbeknown to us. I am not saying there is zero risk. There may be a slight risk. There are a lot of moving parts in a tour such as this and we are trying to control that."

South Africa's would not be the first breach of protocols in the new normal. Last month, West Indies' players were barred from training during their period of managed isolation in New Zealand after sharing food and socialising in hallways, while Pakistan were put on a final warning that they would be sent back home after several similar incidents. Pakistan remain in isolation and have not been granted an exemption to train.

This is South Africa's first experience hosting a bio-bubble - the tour is believed to be worth £3 million to CSA - and they are due for three more this summer, with incoming tours scheduled against Sri Lanka, Australia and Pakistan. It is England's first time in a bubble away from home, having successfully negotiated their home summer with a series of bio-secure environments.

Firdose Moonda is ESPNcricinfo's South Africa correspondent