A youth product of Hvidovre IF, Greko made his senior debut for the first team as an under-19 player against Rishøj Boldklub.[1] On 2 November 2012, he scored a hat-trick after coming on as a substitute in a 2nd Division match against IF Skjold Birkerød.[2] On 15 January 2013, Greko signed a new two-year contract with Hvidovre.[3]
Roskilde
On 8 August 2014, it was announced that Greko would be the new signing of FC Roskilde valid from the new year, as he would become a free agent.[4] There, he was set to be the replacement for Emil Nielsen, who had moved to Norwegian club Rosenborg.[5]
He made his debut for Roskilde on 25 March 2015, in a 0–2 defeat against HB Køge in the 1st Division.[6] A strong six-month stretch for the club, in which he scored 7 goals in 14 appearances and became club top goalscorer that season, attracted considerable interest from Danish Superliga clubs.[5]
Brøndby
On 18 June 2015, Greko signed a four-year contract with Danish Superliga club Brøndby.[7] He made his debut for the club in the Danish Cup, scoring four goals in a 7–0 win over Holbæk B&I.[8]
He made his Superliga debut for Brøndby on 27 September 2015, when he came on the pitch in the 74th minute, replacing Magnus Eriksson in the 1–0 victory against Copenhagen.[9]
SønderjyskE
Greko signed with SønderjyskE on 28 January 2017.[10] He made his debut for the club 17 February 2017 in a 0–3 defeat against Esbjerg fB.[11] On 21 May, he scored his first goals for the club – a hat-trick – to secure a 3–0 win against his former club Brøndby.[12][13]
Lyngby
On 3 August 2020, Greko signed a two-year deal with Lyngby Boldklub.[14] He suffered relegation to the Danish 1st Division with the club on 9 May 2021 after a loss to last placed AC Horsens.[15] On 28 May 2022, Lyngby Boldklub announced that Greko's expiring contract would not be extended, making him a free agent after the 2021–22 season.[16]
Return to Hvidovre
In June 2022, Greko signed with Hvidovre IF, the club where he had started his career.[17] Greko made his debut on 24 July 2022 against Næstved Boldklub, where he also scored his first goal for his new club.[18]
On July 2, 2024, Greko signed a new 2-year contract with Hvidovre, so it now runs until June 2026.[19]