During the 2013–14 season he was loaned to NK Pomorac in Croatia's Druga HNL where he collected 31 caps and managed 17 clean sheets.

He returned to Rijeka following the end of the loan and recorded his official game début on 19 July 2015 against Slaven Belupo.

On 19 July 2019, Sluga joined newly-promoted Championship side Luton Town for a club record fee of €1.5 million, signing a three-year contract.

[7] On 31 January 2022, Sluga joined First Professional Football League club Ludogorets Razgrad.

[8][9] On 17 October 2024, Sluga joined Israeli Premier League club Maccabi Tel Aviv on a contract until the end of the 2024–25 season.