Cristiano Ronaldo, the Portuguese and former Manchester United footballer, is facing a lawsuit seeking “a sum exceeding” $1 billion over his promotion of Binance, the world’s largest cryptocurrency exchange.

A filing in a US district court in Florida claimed that Ronaldo “promoted, assisted in, and/or actively participated in the offer and sale of unregistered securities in co-ordination with Binance.” The plaintiffs claim his endorsement led them to make loss-making investments.

Ronaldo, 38, who plays for the Saudi Pro League club Al-Nassr as well as his national team, signed a multi-year agreement last year with Binance to promote non-fungible tokens (NFTs). These are virtual assets that can be bought and sold and can be used to mark ownership of something, such as a picture or video online.

As part of the deal, the footballer and Binance created an NFT collection last November for sale on the company’s platform which he said would reward fans “for all the years of support”.

Called CR7 after the footballer’s initials and shirt number, Ronaldo said: “It was important to me that we created something memorable and unique for my fans as they are such a big part of my success. With Binance, I was able to make something that not only captures the passion of the game but rewards fans for all the years of support.”

Last week, Changpeng Zhao, 46, the co-founder and chief executive of Binance, pleaded guilty to money-laundering charges and will pay a $50 million fine as part of a $4 billion-plus settlement to resolve a lengthy inquiry by American prosecutors.

The exchange will pay $1.81 billion within 15 months and a further $2.51 billion forfeiture as part of the deal with the justice department, prosecutors said. Zhao personally will pay $50 million.