A rabbi who helped Russian billionaire Roman Abramovich obtain his Portuguese citizenship has been told he cannot leave Portugal and must present himself to authorities when required.
Daniel Litvak was detained on Thursday as part of an investigation into how citizenship had been granted.
The naturalisation process of several Jewish people is being investigated.
On Friday, Mr Abramovich was sanctioned by the UK in response to Russia's invasion of Ukraine.
Mr Abramovich, 55, is the owner of Chelsea FC and he is one of seven oligarchs to be hit with fresh sanctions, including asset freezes and travel bans.
The Premier League has disqualified him as a director of the club.
Mr Abramovich was granted Portuguese citizenship in April 2021 under a law that offered naturalisation to descendants of Sephardic Jews, who were expelled from the Iberian peninsula more than 400 years ago during the Inquisition.
Applicants for Portuguese citizenship via this route are assessed by experts at one of Portugal's Jewish communities in either Lisbon or Porto. Mr Litvak is the rabbi for the community in Porto (northern Portugal) and was responsible for assessing Mr Abramovich's application.
Mr Litvak was detained by authorities as he was preparing to travel to Israel. He was asked to hand over his passport and will have to periodically present himself to authorities.
Portugal's Judicial Police and public prosecutor said on Friday that there were suspicions of money laundering, corruption, fraud and falsification of documents in the process of of granting citizenship to descendants of Sephardic Jews.
Porto's Jewish community has denied any wrongdoing and said it was the target of a smear campaign. They added that Mr Litvak oversaw the department that grants certification of an individual's Sephardic Jewish heritage and the criteria used for granting someone Portuguese nationality had "been accepted by successive governments".