An IAAF source said this meant that if a female British athlete, such as the 400 metres hurdles world and Olympic champion Sally Gunnell, broke the world record, it would not be recognised if Modahl later lost her appeal.
Modahl, whose success in the European Cup was vital to the British women's World Cup qualification, faces a four-year ban after two tests indicated a doping offence. She maintains her innocence, but if she fails to convince the IAAF her punishment will be applied retrospectively from 18 June, when she gave the first urine sample. Her 800 metres victory in the European Cup came a week later.
The British Athletic Federation (BAF) cited natural justice in making their decision - Modahl has been given up to 30 days to prepare her case at a hearing with the BAF.
'To have withdrawn the team at this time could be seen as an assumption of guilt of an individual athlete before it was proven, which could well have the effect of prejudicing that athlete's case and her right to a fair hearing,' the BAF said.
The IAAF Council, which has overall control of the World Cup, is empowered to withdraw the British women's invitation. But they have not gone that far. 'We don't want to go to war,' said an IAAF source.
Relations between Britain and the IAAF have been strained in recent years and some observers have been suspicious about the way notification of positive drug tests on British athletes has coincided with major championships.
The IAAF's statement, addressed to the BAF, said: 'We feel it is our duty to inform you that should the athlete be eventually rendered ineligible according to the IAAF rules and procedure, any result achieved by the British women's team would, regrettably, not be considered valid in the standings of the competition.'
It is an intractable situation for both parties. Yesterday, the British federation stressed that the nine-week delay in notification following Modahl's initial test was 'a significant factor'.
The statement also pointed out that testosterone - present in Modahl's samples in 'astounding' levels, according to the IAAF - is a naturally occurring hormone. 'It should be noted that the presence of testosterone is not in itself an offence,' it said.
Medical opinion is divided on whether such high levels of testosterone could have been produced by a medical condition.
Friends of Modahl said she was very grateful to the BAF for its support.
Meanwhile the two expert witnesses at the second testing of Modahl's sample, Professor Arnold Beckett and the Sports Council's Dr David Cowan, are still awaiting full details of the first test.Reuse content