Sluga is coming off an impressive campaign for Rijeka that has seen him earn his first call-up to the Croatia national squad, with a potential debut for the World Cup runners-up in their upcoming Euro 2020 qualifier against Wales not out of the question.
His crowning moment came on Wednesday when he saved a penalty during his side's 3-1 win over Dinamo Zagreb in the Croatian Cup final.
Dinamo are another club to have shown an interest in Sluga, who has one year remaining on his current contract and as such is set to secure a move away this summer rather than leave on a free in 12 months' time.
Norwich, who have also been linked with a move for Liverpool's reserve goalkeeper Simon Mignolet, are looking to upgrade on current No.1 Tim Krul following their promotion from the Championship.
Daniel Farke's side conceded 57 goals in 46 matches on their way to securing the title in England's second tier, and will need to tighten up at the back if they are to avoid immediate relegation from the top flight.
Sheffield United, meanwhile, are hopeful of securing a deal to re-sign Manchester United goalkeeper Dean Henderson after the 22-year-old's impressive loan spell at Bramall Lane proved key to the Blades' promotion.
No side conceded fewer than the 41 goals offered up by Chris Wilder's team in the Championship in 2018-19, with Henderson confirming himself he is keen to return to South Yorkshire next term.
If a deal cannot be secured with the Old Trafford outfit, however, then Sluga is seen as an affordable alternative.
Derby's interest in Sluga will be solidified if they can secure themselves Premier League football next season with victory over Aston Villa in the Championship play-off final at Wembley Stadium on Monday.
Frank Lampard has led the Rams to the verge of promotion during his first season in charge at Pride Park and has emerged as the frontrunner to replace Chelsea manager Maurizio Sarri should the Italian leave Stamford Bridge for Juventus this summer.