Following his time in England, Zadkovich returned to Australia in late 2005 and trialled for Sydney FC. 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 12-minute debut off the bench against Queensland Roar, Zadkovich impressed with his first start against Perth Glory, playing one game in Sydney's run to the inaugural A-League championship, earning him a two-year full-time contract. He was allowed to leave the club in March 2008.
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. Zadkovich made his Derby debut as a second-half substitute against Norwich City at Pride Park in October 2008, in a match which Derby won 3–1. He struggled with injuries during his time at Derby and, after only 7 appearances for the club, cancelled his contract by mutual consent on 23 January 2010.
On 6 April 2010, Zadkovich confirmed that he had penned a three-year contract with the Newcastle Jets that would see him return to play his football in Australia. Zadkovich played 97 games over four seasons with the Jets. He was appointed captain in his third season and led the team until he was recruited by Perth Glory in 2014.
Perth Glory
On 29 May 2014, Zadkovich received an early release from Newcastle Jets and signed with Perth Glory. On 15 November 2014, Zadkovich made his debut for Perth Glory coming on as a substitute against the Western Sydney Wanderers. Glory went on to win the game 2–1. On 22 November 2014, Zadkovich came on as a substitute against Wellington Phoenix in the 61st minute but was sent off after just 17 seconds with a two-footed tackle. On 8 May 2016, after not playing a single match in the season due to injury, Zadkovich retired from playing football.
Managerial Career
Broadmeadow Magic FC
Zadkovich's first foray as a club manager arose when he was announced as the manager for Football Northern New South Wales club Broadmeadow Magic.
International career
Zadkovich made his debut at right-back in the last home game of 1st round 2010 World Cup Qualifications, against China, at ANZ Stadium on 22 June 2008. Australia lost this match 1–0. Zadkovich took part in the 2008 Olympics as part of Australia's national team. He scored from close range in a 1–1 draw with Serbia, Australia's only goal in an unsuccessful campaign. He also played against Argentina in what was Australia's best performance of the tournament.
