Football star Cristiano Ronaldo is facing a $1 billion class-action lawsuit in the U.S. for allegedly promoting, assisted in, and/or actively participated in the offer and sale of Biance, the largest cryptocurrency exchange in the world.

It is alleged that the Portuguese footballer’s involvement in Biance caused plaintiffs to suffer significant financial losses.

They are seeking damages of “a sum exceeding” $1bn (£790m).

 NFTs are virtual assets that can be bought and sold, but which have no real-world form of their own – in other words they only exist digitally. Generally, they are used to mark ownership of something, such as a picture or video online.

“CR7” refers to Ronaldo’s initials and shirt number and is used as branding in a range of products, from footwear to fragrances, that have helped make him one of the wealthiest athletes on earth.

The claimants allege that Ronaldo’s promotion of Binance led to a “500% increase in searches” for the crypto exchange, which is registered in the Cayman Islands.

They also say it led people to use the firm to invest in what they call “unregistered securities” – such as Binance’s BNB cryptocurrency.

According to the US Securities and Exchanges Commission (SEC), these assets can be considered securities – and so celebrities endorsing them must follow US law.