Once all membership criteria have been met, any step backward will have serious consequences for the continuation of the process, said Verheugen, who is on a two-day visit to Croatia.
The European Union demands of Croatia to fully cooperate with the Hague tribunal and will rely on the tribunal's report in making the assessment which is necessary for the process of Croatia's admission to the EU, Verheugen said.
The EU official added he was confident that a positive report by the tribunal's chief prosecutor, Carla del Ponte, in November would open the door to Croatia-EU membership talks at the beginning of next year.
Commenting on other criteria which Croatia is expected to meet, Verheugen said the country had to solve the problem of refugee return and enable Serb refugees to return to their homes and reclaim their property.
Close cooperation with the European Commission, the UNHCR, the OSCE and the governments of Bosnia-Herzegovina and Serbia and Montenegro will help the Croatian government complete that task, Verheugen said.
He pointed to the importance of conducting an appropriate campaign to acquaint refugees and displaced people not wishing to return with legal possibilities regarding reconstruction and property repossession.
Speaking about the economic criteria for admission, Verheugen said the EC had concluded that Croatia had a functioning market economy and was capable of meeting almost all membership requirements within a reasonable period of time, although there were problems in the area of environmental protection.
The EU Commissioner also commented on the recently adopted pre-accession strategy for Croatia and tried to explain to the MPs what it was about.
After the official opening of the talks, the scanning of the Croatian economy will start, Verheugen said, promising that the EU would continue helping Croatia.
Croatia will be the next country with whom the EU will start membership talks, he said, adding that this was a signal on the pan-European level.
Expressing regret at the instability of the region, Verheugen said Croatia had managed to find its way out of the instability and meet all criteria for the start of membership talks thanks to an energetic process of reforms.
This should encourage countries in the region, he said, calling on Bosnia-Herzegovina, Serbia and Montenegro, Macedonia and Albania to correctly read the signals from Croatia and draw lessons.
Croatia has a new task - to set an example, Verheugen said.
Wrapping up his address, the EC official said Croatia was the last country he was visiting in his capacity as Enlargement Commissioner before taking up office as European Commission vice-president and commissioner for industry and entrepreneurship.
Verheugen was today received by Parliament President Vladimir Seks, who positively assessed the EC's pre-accession strategy for Croatia, stating that it was a good and comprehensive framework for intensifying preparations for EU membership.
Seks said that the Sabor was making efforts to soon appoint its representatives to a Croatia-EU parliamentary committee.
Most laws which needed adjustment to the EU legislation were adopted unanimously thanks to the parliamentary parties' position on EU membership being a strategic goal of great importance, Seks said.
Verheugen said he believed that Croatia was a European country according to its history, culture, and the mentality of its people, as well as that it was well prepared to continue the admission process.
Commending the country for standing out in the region thanks to its own efforts and contributing to regional stability, Verheugen said the EU needed Croatia for setting a positive example as much as Croatia needed the EU.