Scharner spent last season on loan at former club Wigan Athletic, but the midfielder has now returned to German side Hamburger SV.
Bruce has offered the versatile midfielder a two-year contract with Hull, but Scharner is reluctant to leave Germany after promising his wife that they would stay in Hamburg for family reasons.
Scharner is quoted by the Daily Mail as saying: "If Hamburg want to have a war with me, they can have one."
The 33-year-old is surplus to requirements at Hamburg, despite impressing as Wigan claimed a maiden FA Cup success last season.
Across seven seasons in English football Scharner has made 218 appearances for Wigan and West Bromwich Albion.