Students applying for university places in England must be told with "absolute clarity" how courses will be taught - before they make choices for the autumn, says the university watchdog.
Courses might still be online - and Nicola Dandridge of the Office for Students warned against misleading promises about a "campus experience".
University campuses have been closed this term by the Covid-19 outbreak.
But universities can charge full fees even if courses are taught online.
"The important thing here is absolute clarity to students, so they know what they're getting in advance of accepting offers," Ms Dandridge told MPs on the education select committee.
"What we don't want to see are promises that it's all going to be back to usual - an on-campus experience - when it turns out that's not the case," said the chief executive of the Office for Student (OFS).
The OFS says this information should be provided for students before they make a firm choice in June - and "certainly before" the clearing process that follows students getting their A-level grades in August.
If universities have to update plans after students have made a decision, the OFS says universities should release students from any acceptances and allow them to "change their minds".
Applicants this year will be waiting to see whether courses will be taught by distance learning or on campus, or a combination of both - and whether they will have accommodation, which might be limited by social distancing.
Ms Dandridge told MPs that before students make decisions they need to know "what they are getting".
She suggested a likely outcome would be "much greater and more sophisticated use of blended learning so that's face-to-face plus online," she said - and that it must not only be "bunging lectures online".
Universities Minister Michelle Donelan has already said that even if their courses are only taught online, students would still be liable for the same full tuition fee as those being taught in-person.
The University of Manchester has said that its lectures will be online next term - but it wanted to allow small group teaching as soon as safely possible.
Other universities are considering a delay to the start of the autumn term - and there have been suggestions that some more "hands-on" courses will be taught first on campus while others might remain online.
Universities are facing their own cash problems from an anticipated reduction in the number of overseas students.
Debra Humphris, chair of the University Alliance group of universities, said the scale of the financial challenge would not really be clear until the end of the autumn admissions process.
She said support from the government would bring forward existing money to help with cashflow, but "it's not additional funding".
Jo Grady, leader of the UCU lecturers' union, told MPs there needed to be clear guidance from the government on how and when universities should reopen buildings in the autumn - and not to leave decision to institutions in competition with each other.
She warned that financial pressure could mean "some universities will rush to re-open".
"They will want to promise students that they will be re-opening next semester in order to attract those students, rather than have them go somewhere else".
Dr Grady said that university campuses would not be easy places for social distancing - and that lecture halls would bring together "two or three hundred people".
"Students go from cafes to libraries to restaurants - everywhere is always rammed," she said.
A spokeswoman for Universities UK said universities were "already preparing for a range of scenarios - including periods of online study in the academic year 2020-21".
"Institutions will be communicating their plans to prospective and current students in the weeks ahead."