London last week said British ministers and royals would not attend the showpiece in protest over the poisoning of former double agent Sergei Skripal and his daughter in England.
The Skripals survived the nerve agent attack but remain in critical condition.
British Prime Minister Theresa May said her government had found that Russia was “culpable” of the attack — a charge Moscow angrily denies.
England is still expected to send its team and none of the 31 nations that qualified alongside the host have said they would not do so.
But Polish President Andrzej Duda's office said he will be skipping the tournament's opening ceremony on June 14 in Moscow.
“Yesterday, the president made the decision not to participate as a representative of Poland at the World Cup in Russia,” presidential chief of staff Krzysztof Szczerski told RMF FM radio.
Iceland's national broadcaster RUV said the foreign ministry was consulting with its “allies” about a joint diplomatic boycott.
RUV said this possibly referred to Sweden and Denmark because they too are playing in Russia.
“The Icelandic government has not made any decisions on possible measures in the wake of the attack but will continue to elaborate and consult with its closest neighbours and allies,” the foreign ministry said in a separate statement.
Swedish foreign ministry spokesman Per Enerud told AFP on Monday “this is one of many ideas we are looking at”.
The Danish foreign ministry also told AFP that the punitive step was under discussion but that no final decision had been reached.
Skripal's poisoning with a secret Soviet nerve agent designed specifically for assassinations has sparked an increasingly hostile war of words between Moscow and London.
The United States joined Germany and France in voicing support for Britain's position and blaming Russia for the attack.
The Times of London reported on March 10 that UK officials were talking to the US and European allies about a co-ordinated retaliation that could involve a World Cup boycott.
Dignitaries usually attend the opening ceremony and sometimes their country's big matches.
Russian officials reacted to reports of more nations possibly joining Britain with a mixture of anger and sarcasm.
“You can only feel sorry for Iceland's officials — they would have loved to root for their team,” parliament's sports committee chief Mikhail Degtyarev said.
“It is sad to see Iceland become the fodder of an information and political war against Russia.”
Russia's World Cup organising committee chief Alexei Sorokin had earlier said the British no-show would have “no impact on the quality of the tournament”.