Two pilots and nine cabin crew were all held in the Asian island hub, with BA insiders saying they will be stuck there for 21 days.
The crew is understood to have landed in Singapore on Sunday evening on a journey from Sydney, with one case of monkeypox being detected during routine airport testing.
They were set to fly onward to London after a short connection, but new crew had to be found once the case was picked up and the group was put into quarantine.
A British Airways insider told the Daily Mail: “One of them had it, so they impounded the whole crew. Now they have got to spend 21 days in quarantine.
“Everyone has been told not to talk about it – but it’s all everyone is talking about.”
Monkeypox is continuing to spread across the globe, with cases now reported in the US, Canada, Australia, Mexico, Argentina, Morocco, Spain, Portugal, France, Germany, Italy and Sweden.
In Britain, the total number of confirmed infections has now reached 574.
The World Health Organisation (WHO) has traced the sickness to the tropical rainforests of Central and West Africa and defines it as a viral zoonotic disease – meaning it can be transmitted from animals to humans – with the first case recorded in what is now the Democratic Republic of Congo in 1970.
Health officials in the UK are currently examining the link between monkeypox and the gay and bisexual community, following evidence that it is most commonly detected in these groups.
A relatively mild viral infection, the disease has a six to 16-day incubation period and sees patients first suffer fever, headaches, swellings, back pain, aching muscles and a general listlessness in its opening stages.
Once that passes and the fever breaks, the sufferer will experience a skin eruption, in which a rash spreads across the face, followed by the rest of the body, most commonly the palms of the hands and soles of the feet.
A British Airways spokesperson said the risk to others onboard the flight was very low.
They said: “We’re working closely with the Singapore Health Authorities and have offered assistance with any information they require. We’re in contact with our crew and providing the necessary support.”