"The wrong ones, the populists, should not have more power," Lahm said. "The election in the Netherlands is the latest example. The right-wing populists - thank God - were not as strong as was feared.
In the spring, France will vote, in the autumn it's Germany. I think it is important that we not only think about it but above all speak about it."
The Party for Freedom of anti-Islam Dutch politician Geert Wilders won fewer parliamentary seats than had been projected in polls before the election last month, a relief for Prime Minister Mark Rutte and mainstream politicians across Europe who are contending with a rise in anti-establishment movements.
The anti-immigrant party Alternative for Germany (AfD) are polling at around 7 percent after seeing their support fall by more than a third.
The (AfD) on Monday told Bayern Munich's Philipp Lahm, who captained the German national side to World Cup victory in 2014, to focus on soccer not politics.
Germany holds a general election in September and the AfD is expected to enter the Bundestag national parliament for the first time, a worrying prospect for Germans still fearful of xenophobia in politics more than seven decades after the defeat of the Nazis.
"Philipp Lahm should look after his football and leave politics to others as much as possible," Georg Pazderski, AfD leader in the Berlin city parliament, told mass-selling daily Bild.
"If he wants to do politics, he should enter politics and be active there."
Lahm retired from international football after winning the World Cup with Germany in Brazil three years ago. He plans to stop playing altogether at the end of this season with Bayern Munich.
Merkel, who will seek a fourth term in what is expected to be a close-fought ballot, has come under fire for opening Germany's doors to refugees, more than one million of whom - mostly Muslims - have entered the country over the past two years.
Seeking to boost support for the chancellor's conservatives, senior Merkel ally Julia Kloeckner stoked the integration debate at the weekend by calling for stricter rules for Islamic preachers and a ban on foreign funding of mosques.
Merkel's spokesman Steffen Seibert dismissed the idea, which Kloeckner - who is deputy leader of the chancellor's Christian Democrats (CDU) - and other senior party members want to enshrine in an Islam law.
"Such a law is now not an issue for government business," Seibert told a news conference, stressing the high regard Merkel's ruling coalition has for religious freedom in Germany.
While stopping short of calling for an Islam law, Merkel said in her weekly podcast on Saturday that refugees in Germany must respect tolerance, openness and freedom of religion.
The message backed up a less compromising tone on integrating migrants that Merkel set at a CDU party conference in December, when she called for a ban on full-face Muslim veils "wherever legally possible".
By talking tougher on integration, Merkel is also seeking to reclaim support her party lost last year over her refugee policy to the anti-immigration Alternative for Germany (AfD) party, which punished the CDU in regional elections in 2016.
The AfD has lost voter support this year, hurt by infighting that has sent its ratings down to around 7 percent from a high of 15.5 percent at the end of 2016.
In the Netherlands, Prime Minister Mark Rutte used a similar tactic to win re-election this year, seizing back the initiative from anti-Islam populist rivals by matching some of their tough rhetoric on immigration.
He told the country's half-million ethnic Turks that they should integrate and accept Dutch views on freedom of speech or "get lost" after some had been filmed behaving aggressively toward a reporter during a demonstration.
"Our norms and values are all or nothing: you can't pick and choose," he said in response to the footage in an interview last September.
(Additional reporting by Thomas Escritt in Amsterdam; editing by John Stonestreet)