Switzerland captain Granit Xhaka is under investigation by Swiss prosecutors over allegations he obtained a forged Covid-19 vaccination certificate.

The 33-year-old is alleged to have obtained the certificate in 2022, when it was a requirement in Switzerland for some travel abroad.

The public prosecutor's office of the city of Lucerne confirmed that an investigation was underway to determine whether any criminal behaviour occurred in obtaining a "false or forged" certificate.

The Sunderland midfielder, who was playing for Arsenal at the time, posted a statement on social media on Monday saying he had a "mistrust" towards the vaccine and had been "influenced by worries and uncertainty".

He said: "In this troubled state of mind, I acquired a vaccine certificate instead of clarifying my unanswered questions in the proper way.

"Today I see clearly that this way was not correct. It was a mistake. I'm sorry.

"I take responsibility for this decision and will engage with the process of establishing the facts and fully co-operate with the relevant authorities."

The Swiss Office of Public Health confirmed that while there was never a general legal requirement to obtain or hold such a certificate, it was needed for access to various activities, venues and travel, meaning that participation was restricted for anyone who did not possess one.

These measures in Switzerland were in place until spring 2022. After that point, Covid-19 certificates continued to be issued, primarily to enable members of the public to meet entry requirements when travelling abroad.

It is unclear what punishments Xhaka could face, but in 2023 the then Switzerland men's ice hockey coach Patrick Fischer was found guilty of using a fake Covid-19 certificate to work at the 2022 Winter Olympics ‌in Beijing.

Fischer was fined 38,000 Swiss francs by a criminal court. In April this year, he was sacked from the Switzerland job and earlier this month, he was banned for four years by the International Ice Hockey Federation.

The Swiss Football Association said Xhaka, the country's record appearance holder with 152 caps, had withdrawn from the Swiss camp for their upcoming Nations League matches against Scotland, North Macedonia and Slovenia following his statement.

It added the decision to withdraw had been made jointly by the player and management and that they would discuss Xhaka's future with the team after the international window.

Switzerland have away fixtures against North Macedonia and Scotland on 26 and 29 September, before facing Slovenia and North Macedonia at home in early October.

Sunderland boss Regis le Bris refused to comment on the allegations following the Black Cats' defeat at Manchester City on Sunday.

"It is not my area to speak about those problems or situations," he said. "My area is football. About football, he is really good."

Xhaka captained Switzerland at the World Cup earlier this year, where they were knocked out in the quarter-finals by eventual runners-up Argentina.