A steep decline in foreign students coming to study at UK colleges and language schools has prompted fears of a knock-on effect on universities.
The latest figures show a 46% drop in visas for these types of students, a large chunk of whom go on to study degree courses at UK universities.
A key provider of foreign students to UK universities, Study Group UK, says the drop is a real cause for concern.
The government says many language students now come on visitor visas.
These were not included in the latest migration figures but the Department for Business, Innovation and Skills said there had been a 6% rise in the 11-month visas. It also pointed out that university applications from non-EU students were 5.5% up on the previous year.
Overall, the Office for National Statistics data shows net migration to UK has fallen by more than a third.
A net total of 153,000 migrants came to the UK in the year to September 2012, down from 242,000 in the previous year.
It comes after steps to tighten student visa rules required applicants to have better English language skills than in previous years and also required face-to-face interviews between potential students and colleges.
Study Group UK's managing director for higher education James Pitman said: "Today's international FE and English language students are tomorrow's university students and a drop of almost half in visa applications here is real cause for concern. Even conservative estimates suggest 40% of international students arrive at universities through FE and independent pathway routes.
"This supply is being slowly strangled and is a catastrophe waiting to happen for UK higher education."
He added: "It's quite right that abuse of the student visa system be stamped out. But, finding itself without the proper migration exit data required to address the issue precisely, rather than make considered reforms, the government has reached for the sledgehammer to crack this particular nut.
"The modest increase in university sponsored visas may give the illusion that all is well, but it simply reflects applications from non-EU students who have been in the country for years already, taking GCSEs and A-levels in preparation for higher education study."
Study Group works with about 20 UK universities to deliver pathway courses in which foreign students follow English language and foundation year courses either alongside or ahead of their degree courses to help acclimatise students to studying in the UK.
A spokeswoman for the Department for Business, Innovation and Skills denied that the tightening of visa rules for students would have a knock-on effect on universities, saying its strategy was to eliminate abuse and focus on the high quality, high value sectors.
"We are achieving our aim, as sponsored visa applications fell to 46%, 46% and 7% respectively for the further education sector (tertiary, further education or other colleges), English language schools and independent schools.
"The latest University and College Admissions Service figures show applications from non-EU students are currently 5.5% higher than this time last year."
The Higher Education Statistics Agency (Hesa) figures for the year 2011-12 show a 1.5% increase in the total number of non-EU students at UK universities while the number of UK domiciled students fell 0.6%.
She added: "We want to attract more world-class individuals with the knowledge and expertise that will drive leading research and economic growth. However we have reformed the student visa system because it has been abused for too long, with providers selling immigration, not education."
But Sarah Mulley, associate director of think-tank the IPPR, said the fall in reducing net migration was largely driven by declining numbers of non-EU students.
"This decline in international student numbers comes at considerable economic cost to the UK at a time when we can ill afford it," she said.
She added that because most students stay in the UK only for a short time, reduced immigration now will mean reduced emigration in the future.
"For example, the latest research suggests that only 18% of student migrants are still in the UK after 5 years."
Chief executive of Universities UK Nicola Dandridge said: "Despite these figures indicating a rise in the number of university-sponsored visas, more recent data from universities show that new enrolments, the clearest indicator of future numbers, have remained broadly flat this year.
"University data also show a mixed picture, with some specific drops from countries such as India and concern about a decline in the number of international post-graduate taught students."
But she added that it was too soon to assess the exact impact of the government's immigration reforms.