Born in Fairfield, Sydney, New South Wales,[1] Zadkovich had previously played for English Football League club Notts County, scoring on his debut against Chester City,[3] as well as Queens Park Rangers and Australian side Wollongong Wolves.

He travelled with the squad to the FIFA Club World Championship and despite not making an appearance he impressed coach Littbarski, being called in as a short-term replacement for injured Ufuk Talay late in the season.

After a 12th-minute debut off the bench against Queensland Roar, Zadkovich scored on his first start, against Perth Glory, during Sydney's run to the inaugural A-League championship, earning him a two-year full-time contract.

On 17 April 2008, it was revealed Zadkovich had signed a two-year deal with English club Derby County, although his registration was unable to be completed before 1 July.

On 6 April 2010, Zadkovich confirmed that he had signed a three-year contract with the Newcastle Jets which would see him return to play his football in Australia.

[7] Zadkovich made his debut for Australia at right-back in the last home game of the first round of the 2010 World Cup qualifications, against China, at ANZ Stadium on 22 June 2008.

During the 2022–23 season, news surfaced that Zadkovich had punched midfielder Giordano Colli during training, with the coach moving quickly to dispel any notion of a rift.