One of Apple's main rivals, Creative Technology, has been awarded a patent in the US for the interface used on many digital music players.
Creative said the patent applied to its players, as well as some competing products such as the Apple's iPod and iPod mini.
The patent covers how files on a music player are organised.
Creative was one of the first companies to produce MP3 players but has lost out to Apple which dominates the market.
The Creative announcement is the latest salvo in its self-declared war against Apple.
In November, Creative boss Sim Wong Hoo said he aimed to out market his competitors, saying the MP3 war had started.
Apple's iPod is estimated to account for 80% of sales of digital music players which use hard drives to store music.
Navigate music
Creative said it had applied for the patent, dubbed the Zen Patent, on 5 January 2001 and was awarded it on 9 August.
It applies to the way music tracks are organised and navigated on a player through a hierarchy using three or more successive screens.
For example, this would be a sequence of screens that could display artists, then albums and then tracks.
"The first portable media player based upon the user interface covered in our Zen Patent was our Nomad Jukebox MP3 player," said Creative CEO Sim Wong Hoo.
"The Apple iPod was only announced in October 2001, 13 months after we had been shipping the Nomad Jukebox based upon the user interface covered by our Zen Patent."
In its press release, Creative said Apple had filed for a patent for a user interface in a multimedia player in late 2002, but its application had been recently rejected.
Creative is looking to take a slice out of Apple with its new products. It recently introduced a new version of its Zen model which has a colour screen and can play video.
"We consider it a dead certainty that Creative will go after Apple for royalties or some other type of compensation for what Creative will assert is infringement of its patents, currently and in the past," analyst Phil Leigh of Inside Digital told the Reuters news agency.
But Mr Leigh added that Creative was likely to have a hard time to get anything out of Apple as the applicability of patents was often difficult to prove.
