Bernard Tomic says he has never "really tried" throughout his tennis career, adding that he has probably been operating at "around 50%".
The Australian claimed he was bored during his straight-set defeat by Mischa Zverev at Wimbledon on 4 July.
A series of lacklustre displays has seen the 24-year-old drop from 17 in the world last year to 73.
"Tennis chose me. It's something I never fell in love with," Tomic told Australia's Channel Seven.
"Throughout my career I've given 100%. I've given also 30%. But if you balance it out, I think all my career's been around 50%.