Vitaly Klitschko has vacated his World Boxing Championship belt but has been named champion emeritus, leaving the door open for the leading Ukraine politician to one day return to the ring.
Klitschko, the reigning WBC champion, is unlikely to box again as he joins thousands of protesters in weeks-long demonstrations against the government in Kiev.
The 42-year-old has won 45 fights with 41 of them knockouts and has only lost twice.
His most recent fight was in September last year.
His younger brother Vladimir holds all the other major world heavyweight titles.