A British exit from the European Union could trigger similar moves by other member states in Eastern Europe, Luxembourg Foreign Minister Jean Asselborn said in a German newspaper interview published on Sunday.
Britain votes on June 23 on whether to stay in the 28-member bloc, a choice with far-reaching consequences for politics, the economy, defense and diplomacy on the continent.
"It cannot be ruled out that Brexit leads to a domino effect in Eastern Europe," Asselborn told Tagesspiegel am Sonntag.
It had been a "historic mistake" from Prime Minister David Cameron to even think about calling a referendum about Britain's membership of the European Union, Asselborn added.
Even if Britain should decide to stay in the EU, "this would not solve the problem that results from the negative attitude of the British toward the European Union", Asselborn said.
Asselborn said he sometimes had the impression that Cameron and the head of Poland's ruling Law and Justice party (PiS), Jaroslaw Kaczynski, had a silent agreement on rolling back European integration.
"Both seem do have the same agenda regarding their critical stance toward the EU," he added.
Since winning elections last year, Poland's conservative and eurosceptic government has clashed with EU regulators on a range of issues, including freedom of speech and democracy as well as energy and environment issues.
Poland is the biggest economy in the EU's eastern wing and the largest recipient of structural funds in the bloc.
Britain, on the other hand, is transferring more money to Brussels than it is getting back, which is one of the arguments of the Leave camp to vote for Brexit on Thursday.