Paris’s public prosecutor has opened an investigation into the racist abuse and online harassment of the French judo star Teddy Riner after he expressed concern about the rise of the far right.

Riner, who has often been voted France’s most popular sportsperson and is one of the most successful judo competitors of all time, told a TV sports show this month that he felt “anxiety” about the rise of the far right in France. Numerous racist insults and hate messages were subsequently directed at him online, the prosecutor’s office said.

The far-right, anti-immigration National Rally (RN) party politician Marine Le Pen is polling high ahead of next spring’s presidential election.

The French football team captain and Real Madrid player, Kylian Mbappé, was at the centre of a row in May when he expressed concerns that Le Pen’s party could win the presidential election.

Riner, 37, who was born on the French Caribbean island of Guadeloupe and grew up in Paris, has a massive following in France, where his ability to swiftly throw and pin his judo opponents to the ground made him a star the Paris 2024 Olympics. He is a French gold medal hope for the 2028 Los Angeles Olympics.

Riner wrote on social media on Thursday: “Debate and contradiction are legitimate. Hatred and racism are not.”

Earlier, he told the state broadcaster France 2 he would continue to speak out. “I grew up in a France where people in difficulty were close-knit and united. Today’s attempts to divide France, to create an mood of instability are unfamiliar to me. What will we leave for our kids tomorrow? The France I want is the France I grew up in where everyone knew how to live together.”

In May, Mbappé, 27, who grew up in Paris’s northern suburbs in a family with Algerian and Cameroonian heritage, was criticised by RN party figures after he told Vanity Fair: “I know what it means and what consequences it can have for my country when people like them come to power.”

Le Pen told RTL radio at the time that she found it reassuring that Mbappé did not want her party to win, because his own strategy of leaving Paris Saint-Germain in order to win at Real Madrid had not worked. “Frankly I think football fans are free enough to know who to vote for without being influenced by Mbappé,” she said.

Julien Odoul, an RN MP and party spokesperson, said that Mbappé, as the captain of the French men’s team, must represent all of France including the millions of RN voters, and should not become a “political activist”.

Riner wrote on social media: “Being a high level sportsperson does not stop you keeping your feet on the ground and having an attentive eye on your country.”

He said he shared many French people’s concerns about the “current situation” in France – describing what he called rising anger, people struggling to make ends meet, plummeting respect for institutions, the fragility of the French education system and lack of perspective for young people.

Riner wrote: “I love France deeply – I’m defending its history, its talent, its heritage, its republican values and its diversity.”