Beckham has appeared in a worldwide advertising campaign for Vodafone, which also sponsors his old team Manchester United.
As part of its sponsorship deal, Siemens can choose one of Real Madrid's players to front its ad campaign. Because Beckham is now the club's highest profile star, it would most likely be him.
If this is the case, there are concerns that Siemens may feel its sponsorship of the club is undermined by the star being so closely linked with another brand associated with mobile phones.
Beckham has been in a similar situation before. As well as appearing in Vodafone ads, Beckham also fronts campaigns for Adidas, causing tension with Man Utd kit sponsor Nike, which has previously featured other United players in its ads.
It is thought that if Siemens applies pressure to Real Madrid, Beckham's deal with Vodafone may have to end. However, how this would be achieved is unclear, because buying out Beckham from his Vodafone contract would come at a high price.
Beckham is one of the most sponsored football players in the world. He has a range of clothes, called DB07, at Marks & Spencer in a deal worth 拢3m a year, a 拢2m-a-year deal to promote Pepsi and a 拢500,000 deal to endorse Castrol oil.
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