The 'Poison' hitmaker and the 'Fantastic Beasts: The Crimes of Grindelwald' star are in the rock supergroup The Hollywood Vampires - along with Aerosmith's Joe Perry - and Cooper gets the impression that Depp enjoys being on stage and rocking out more than playing a character on the big screen.
Although, he's told him ''not to lose the day job'' because he can't earn ''$25 million'' a show.
Praising the 56-year-old star's guitar playing and commitment, Cooper said: ''Johnny gets up there and plays his butt off.
''He's there for rehearsal before I get there.
''People are really surprised when they hear him play because they don't realise how good of a guitar player he is.
''I think he'd rather play guitar than act.
''I told him not to lose his day job, because we can't pay him $25 million a show, but I think he loves playing guitar and he loves being up on stage.''
The 71-year-old shock rocker also admitted that he himself feels ''a lot of freedom'' being in the band because he doesn't have to be the frontman all the time.
He said: ''It's kind of nice that I'm not always the frontman.
''I can move around and other people can take the lead.
''To me, that's a lot of freedom.''
The 'Feed My Frankenstein rocker - whose real name is Vincent Furnier - says it's also nice for him to not have to be in character in the Vampires.
He told Tommy Sommers of 'Three Sides Of The Coin': ''That band is great because I don't have to play Alice Cooper in that band.
''I'm the lead singer. Alice will never talk to the audience [during solo performances] until the very end of the show, whereas Alice in the Vampires talks to the audience all night. If we do a Doors song, I'll tell them a story about Jim Morrison. If we do a Who song, I'll tell them a story about Keith Moon.
''You have a wealth -- all those stories, and the audience wants to hear that.''
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