The Republic of Ireland 'B' international signed for the Black Cats a year ago from Cork and could join Leeds on a season-long loan.
O'Donovan signed for Sunderland for an eircom League record transfer fee of €500,000 in August last year.
The fee could increase to €1m depending on appearances for club and country. O'Donovan is understood to have signed a 3-year-deal, worth €8,000 per week.
He made his Premiership debut for Sunderland against Birmingham City on August 15, 2007 when he came on as a substitute in the 69th minute. He made his first start of the season in the 3-1 defeat to West Ham United.