The Government's overhaul of careers advice will "reduce substantially the overall capacity to deliver career support" for young people in FE colleges, according to a report.
The study by experts at Derby University, published today, claims there has been a lack of strategic planning for the changes coming into effect next month.
The report argues that FE colleges are being marginalised by the new market in careers support that is being created, which instead focuses on the needs of schools.
Discretionary funding for Connexions is being cut by many cash-strapped local authorities. The new "all-age" National Careers Service (NCS) will primarily focus on over-19s, with schools required to provide independent advice for students.
The study argues that 16 to 19-year-olds attending FE colleges, schools and sixth-form colleges will be left at the mercy of a "postcode lottery", with the level of provision dependent on decisions made by individual local authorities and institutions.
In the new report, Dr Tristram Hooley and Professor Tony Watts argue that confusion about the new arrangements is "rife", and have calculated that 2,600 jobs will be lost in the careers guidance sector.
"At present, no publicly visible plan exists to indicate how this messy interim situation will be resolved," the study says.
The report adds: "There has been very limited transition planning at national level: this has led to considerable local confusion. In particular, there is continuing confusion about the future relationship of remaining face-to-face Connexions services to the NCS, and about the branding of such services."
The authors also call for clarification on the NCS's involvement with schools and whether its role is purely strategic or it will become a "delivery body" operating in competition with other careers services.
The research has also found that careers staff have been made redundant in at least 105 local authority areas, with Connexions offices closing in 50.
Careers services are being downscaled in 65 areas, and 40 local authorities are developing their own advice service for young people which schools will be able to buy into.
Many schools, the report says, are "unclear" as to their new responsibilities and how they will fund a service that was previously free of charge.
"It is unclear how much resource schools will be able and willing to allocate to career support services, but it seems likely in most cases to be much less than previous provision," it adds.
The report also criticises the "inelegant" temporary redirect page which appears on the Connexions Direct and Jobs4U websites for being confusing to visitors.
A separate report out this week from the Royal Society of Arts (RSA) recommends that the new careers service make specific provisions to ensure FE colleges offer comprehensive, accurate advice.
A Department for Education spokeswoman said: "The new National Careers Service from April 2012 will offer young people a single point of access to online and helpline support.
"It is down to local authorities to decide how best to fulfil their statutory duty to support young people's education or training - they are accountable to their local communities and should front up for the decisions they take."