Johnny Depp is struggling to master horseriding on the set of his latest film.

The 49-year-old actor - who recently split from the mother of his two children Vanessa Paradis - is currently shooting 'The Lone Ranger' but insiders say he has not yet got to grips with his animal co-star.

One said: ''It has become a problem for Johnny. He wants to do all his own stunts, but he's been falling off his horse so often that producers worry he's going to do permanently damage his tailbone.''

Johnny - who plays Tonto in the upcoming blockbuster - is refusing to use a stuntman and is also growing increasingly frustrated as co-star Armie Hammer is a natural at horseriding.

The source added to National Enquirer magazine: ''He sees Armie doing everything so easily, and that's got him even more frustrated.''

Johnny recently revealed the make-up and appearance for Tonto was based on a painting by artist Kirby Sattler.

He said: ''I'd actually seen a painting by an artist named Kirby Sattler, and looked at the face of this warrior and thought, That's it... The stripes down the face and across the eyes... it seemed to me like you could almost see the separate sections of the individual, if you know what I mean.''