|Date of birth||14 May 1993|
|Place of birth||Zagreb, Croatia|
|Height||1.92 m (6 ft 4 in)|
|Current club||Dinamo Zagreb|
|2012–2013||→ NK Rudeš (loan)||30||(0)|
|* Senior club appearances and goals counted for the domestic league only and correct as of 17 August 2013.
† Appearances (Goals).
Zelenika is the product of Dinamo Zagreb youth academy.
Zelenika joined up with the senior Dinamo Zagreb team in 2011. Zelenika was loaned to NK Rudeš, Dinamo Zagreb's feeder team, for the 2012-13 Druga HNL season and almost instantly established himself as the first choice goalkeeper. Rudeš finished third in the league that season. Zelenika rejoined Dinamo Zagreb in the summer of 2013.
In July 2013, after an abrupt departure of Pablo Migliore, Zelenika was recalled by Dinamo Zagreb's manager, Krunoslav Jurčić. As of 30 July 2013, Zelenika has made a debut in, both domestic league (against Rijeka) and in UEFA Champions League 2013-14 qualifying stage (against Sheriff Tiraspol), making him the youngest goalkeeper to achieve such a feat in Croatian football history.
On 7 August 2013, in a match against Sheriff Tiraspol, in UEFA Champions League 2013-14 qualifying stage, Zelenika was included in the starting line-up. Having preformed admirably in both the domestic league and UEFA Champions League, both the team's staff and Croatian press were satisfied with his performance. Zelenika quickly established himself as the team's first-choice goalkeeper, despite team's staff initial intention to name Grzegorz Sandomierski as such.
On 21 August 2013, Zelenika conceded two goals, both in the second half of the first leg of UEFA Champions League 2013-14 play-off round, against Austria Wien. This marked the end of Dinamo Zagreb's clean sheets in the UEFA Champions League 2013-14 qualification phase.
With arrival of Branko Ivanković, Dinamo Zagreb's new manager, Zelenika once again established himself as the side's first choice goalkeeper, and debuted in the 2013–14 UEFA Europa League group stage in the starting line-up against Chornomorets Odessa. Zelenika conceded two goals in that match, both in the second half.
On 23 August 2013, it was announced that Zelenika made the short-list for Croatia U-21 football team for a 2015 UEFA European Under-21 Football Championship qualifying match against Ukraine U-21 footbal team on 9 September 2013.
Zelenika debuted for Croatia national under-21 football team on 9 September 2013 in the starting line-up.