The recommendation will come in annual progress reports, which the European Commission, the EU's executive arm, will publish on 9 November on all the Western Balkan countries, Turkey and Iceland.
The Commission is also expected to deny candidate status for now to Albania. The report will not change the status of Serbia, which will face Commission scrutiny over the next year after submitting its application less than a year ago.
"It's the most likely scenario," said the official. "It's too early for Albania. And Montenegro will likely get candidate status but is not ready to start talks [...] because of concerns over corruption."
Winning candidate status is the last step before a country aspiring to join the EU starts accession negotiations, a long process aiming to align its laws with EU rules and standards.
Hopefuls need to prove their economic reforms are well advanced on the path to becoming functioning market economies and demonstrate substantial efforts to overcome crime and introduce the rule of law.
Montenegro, with a population of 700,000, and Albania are both struggling with rampant corruption.
The EU, a 27-nation bloc of half of a billion people, is already holding membership talks with Croatia, Iceland and Turkey, while all the countries of the Western Balkans want to join one day.
Macedonia is also a candidate but a spat with EU member Greece over its name is blocking the start of talks.
(EurActiv with Reuters.)