The health plans have still to be ratified
The right to access healthcare across Europe could worsen health inequalities if patients are not given the right advice and support, peers say.
The European Commission has put forward proposals to make it easier for EU patients to go abroad for treatment.
But the House of Lords' EU Committee said the rich and educated would be advantaged unless fair funding and information systems were put in place.
Patients' groups are also concerned about the issue of access.
The commission unveiled its plans last year, although it will be several years before they come into force as they need to be ratified by EU leaders.
Under the proposals, patients would be able to claim up to the amount their treatment would have cost in their home country.
The commission acted after several court judgements in favour of patients seeking treatment outside their home country.
In particular, a European Court ruling in 2006 said the NHS should reimburse a woman for a hip replacement operation she had in France.
Currently, only emergency treatment is offered routinely on a cross-border basis, although the NHS does pay for care abroad where patients face an "undue delay".
However, the numbers applying under this system only reach a few hundred each year because of the progress made over waiting times in recent years.
The European proposals go much further than this system by placing the onus on a health service to justify blocking treatment abroad.
They were designed to allow patients the choice to access the best and quickest possible specialist care.
The Lords committee welcomed the move, but said certain safeguards needed to be put in place.
It said doctors and dentists needed to be given responsibility for explaining to patients about their entitlements.
To help them do this, the committee said member states should be compelled to provide information on how their health systems work.
The report also said funding mechanisms needed to be resolved - as yet there is no firm agreement on what should be done.
It called for NHS trusts to pay for the treatment rather than expecting patients to fund it and then apply for a reimbursement as the initial financial outlay could act as a disincentive to many.
Baroness Howarth of Breckland, chairman of the panel which looked at the issue, said: "All EU citizens, not just the wealthy or well informed, must be able to benefit."
And Katherine Murphy, of the Patients Association, added: "You need access to good information and our concern is over who will provide this.
"Without this most people will not feel comfortable making the choice and it will just end up something that is used by the few."
Paula Pohja, of the consumer group Which? added: "Seeking healthcare treatment abroad shouldn't be an ordeal.
"Consumers need clear information and assistance."
A Department of Health spokesman said the government welcomed the report.
He added: "We will be considereing the reporrt's findings carefully and the government will respond formally in due course."