During his second season in the first team, Rajković's reputation grew so such that in November 2005, English Premier League club Chelsea decided to pay €2 million for the 16-year-old centre-half.

Under the terms of the deal, Rajković stayed at OFK Beograd as a loaned player from Chelsea until the end of the 2006–07 Serbian SuperLiga season.

[3] On 23 August 2010, Rajković transferred to another Eredivisie club, Vitesse, together with his former Chelsea teammates Nemanja Matić and Matej Delač on a season-long loan.

On 27 January 2020, after six months of inactivity, Rajković signed a two-and-a-half-year contract with Serie B club Perugia as a free transfer.

[10] By the age of 16, Rajković was a regular in the Serbia under-21 national team, later becoming the youngest player ever to appear in a qualifying match of the UEFA European Under-21 Football Championship.

[11] On 17 June 2007, during the 2007 UEFA European Under-21 Football Championship, which the Serbia U21 team eventually finished as runners-up in, Rajković was part of a controversial second goal for England.