Construction will be one of the first subject areas for Diplomas
Fewer than four in 10 university admissions officers see the vocational Diploma as a "good alternative" to A-levels, a survey suggests.
The government wants Diplomas, set to be launched next year in England, to be a qualification that will allow students to find places at university.
Of those polled, 38% saw Diplomas as a suitable alternative, while 88% backed the International Baccalaureate.
ACS International Schools polled about one-third of admissions officers.
Its telephone survey also found that 33% of those questioned backed the forthcoming "Pre-U" exam.
The survey found that 41% of the admissions officers saw the Diploma as a "positive step forward", while the remainder either thought that it was not a step forward or did not know.
A majority of respondents also said that they thought the new qualification would result in a "two-tier system".
However, 70% of admissions officers questioned supported the principle of offering a wider range of qualifications, beyond the traditional A-level.
The response of universities towards the Diploma has been seen as important in establishing the credibility of the new qualification.
On Wednesday, Schools Secretary Ed Balls said that he wanted the Diploma to be available as a pathway to the top universities.
IT and media
The qualification is intended as a different type of qualification, linked to industry and providing an alternative to the academic A-level.
The first courses will be in construction, engineering, health, IT and media.
But the previous education secretary, Alan Johnson, had warned that the plans for a system of vocational qualifications "could go horribly wrong".
Mr Johnson later said the comment had been the "cardinal sin of giving a straight question an honest answer".
The survey was commissioned by ACS International Schools to see which qualifications would be most likely to be welcomed for university admissions.
Responding to the survey, a Department for Children, Schools and Families spokesperson defended the Diploma.
"As Ed Balls said earlier this week, we have been working with employers and universities in designing the Diplomas to offer choice and opportunity and to ensure they meet the needs of both employers and learners."
"Also this week, the draft for the new engineering diploma was welcomed by university vice chancellors and the engineering employment sector."