England's teacher training authority is stressing there is a quick route into teaching for exceptional candidates.
David Wolfe is an eminent physicist who has retired to the UK
The development followed reports that a school was fighting to keep a highly experienced American physics professor, David Wolfe, on its teaching staff.
Tim Dingle, head of the Royal Grammar School in High Wycombe, Buckinghamshire, said he had been arguing the case for a year.
He said on Tuesday that there were signs that a solution was in sight.
Dr Wolfe has been teaching at the school for two years.
The rules are that he should have "qualified teacher status" (QTS).
Part of that is a requirement to have at least a grade C in a maths GCSE or - Department for Education and Skills officials stress - an equivalent qualification.
There can be no compromise on the need for the QTS, but it is open to training providers who award it to say that teaching for many years in a prestigious university, for example, is good enough.
David Wolfe is emeritus professor of physics at the University of New Mexico, where he used to run the physics department. He has a PhD from the University of Pennsylvania.
He said it would be easy for him to pass a maths GCSE - a qualification for 15 year olds - but, at 65, he was too old for that sort of thing.
"If there's one thing that a person who becomes a professor has done, we may not be the cleverest but we've passed a lot of exams and I've taken enough in my life," he told BBC News.
He accepts there need to be standards for teachers.
"But there also need to be exceptions made in special circumstances, especially given the situation where there is a great lack of teachers in a given subject like physics or maths."
Both are officially "shortage subjects" and the government offers people incentives to train or re-train to teach them.
The school's headmaster, Tim Dingle, said: "It's a ridiculous situation, that somebody of David's skill and inspirational teaching should be put in this situation."
It was, he said, "farcical".
"One couldn't wish for a better teacher than David. Let's keep him in schools, let's keep him teaching children about physics and the joys of it."
The Teacher Training Agency (TTA) says a flexible assessment-only route, to give it its official title, has existed since 2000 for precisely this sort of situation.
Anyone who called its advice line would be told about it, if they seemed to be likely candidates.
A total of 84 people followed this route into teaching last year.
On Monday, the same message went out to Tristram Jones-Parry, set to retire as head of the independent Westminster School, who had wanted to teach maths in a state school - but was told he was not sufficiently qualified.
Instead of having to complete the usual one-year PGCE course, people with suitable skills could be assessed on an individual basis, a TTA spokeswoman said.
This could be done in as little as a day.
She said someone from the agency had contacted the Royal Grammar School on Tuesday to explain the process.
But Mr Dingle says he had been told specifically by the General Teaching Council for England (GTCE), which registers teachers, that there was no flexibility.
He also said he had had a letter from the School Standards Minister, David Miliband, to the same effect.
On Tuesday, Mr Miliband said: "We want high calibre people to become teachers wherever they come from."
There were extensive, rapid and flexible routes to Qualified Teacher Status.
"The Teacher Training Agency will be able to outline these options to anyone interested in joining the state sector. They will find a warm welcome."
A spokesperson for the GTCE said it had advised Dr Wolfe of the Teacher Training Agency's Overseas Trained Teacher Programme, which provided an opportunity to gain QTS while working in a school.
"We receive a large number of enquiries about Qualified Teacher Status and always advise someone without QTS who wishes to teach as a qualified teacher in a maintained school to contact the Teacher Training Agency to find the most flexible route available to gain QTS.
"If we weren't sufficiently clear about this when we spoke to Mr Dingle, Mr Wolfe's Headmaster, we apologise."