The defender joins RBL on-loan for the remainder of the season. The deal doesn't include a permanent option.
Nedeljkovic said, "I'm delighted to be joining RB Leipzig. From the moment the club first reached out, I knew that I wanted to take this opportunity because as a club, they prioritise young players and give them an opportunity to develop.
"2024 wasn't the best year for me, which is why I'm eager to show what I'm capable of here, earn match practice and help the club achieve their goals. I will give it my all right from my first training session!"
RBL chief Marcel Schafer also stated: "We wanted to add further reinforcements to our squad in preparation for the months to come. Kosta is the prime example of a full-back who works hard on the right wing, in addition to bringing speed, an attacking mindset and an excellent mentality to the table.
"He is strong in the tackles, good at winning possession and has an excellent understanding of the game. Kosta has a lot of potential and we will provide him with the opportunity to realise it."