Lars Ulrich thinks Metallica are getting too old to play 'Master of Puppets'.

The 52-year-old drummer has warned that the metal band's days of performing the title track from their 1986 album may be numbered.

He told Billboard: ''Whether we'll be able to play 'Master of Puppets' in our 70s, I just don't know. With Metallica, there's a physicality and a weight that has to be part of it. You can play it less heavy, slower - or you can realise that the music deserves that physical approach, and if the physical delivery isn't there, then maybe it's better not to do it.

''You're trying to prevent something from going off the rails. We're lowering the percentages of [body parts] breaking mid-show.''

The band - whose other members include frontman James Hetfield, 53, guitarist Kirk Hammett, 53, and 52-year-old bassist Robert Trujillo - formed in 1981 and are set to release their 10th studio album.

And although they're getting older, Lars says he has been inspired by The Rolling Stones, especially their 75-year-old drummer Charlie Watts.

He added: ''The only O.G. drummer... the only road map is Charlie Watts. I can see [playing live] in my 70s, mentally, but I just don't know about the physicality. That remains the great question mark.''

Lars recently revealed how he found it easier to be part of a ''collective'' when he was younger as he and his bandmates shared the same values.

He explained: ''It's harder to be part of a collective when you're older.

''When you're 22, you all wear the same clothes, drink the same beer, do the same crazy things.

''Then, all of a sudden, you're in your 30s and 40s and everything has changed.''