The Nigerian center developed as a player at the Ratgeber Academy in Hungary from the age of 14 years old. Nnaji arrived in Barcelona aged 16, completing his youth development with Barça Atlètic.
He started training with the first team on arrival given his physical condition and because he is quick to learn.
In November 2021, he became the youngest Barça player to debut in the EuroLeague, aged just 17 years and 3 months old.
Nnaji is very formidable in the area and his presence means many blocks and great goal protection. He is constantly developing and learning, and despite a height of 212 centimetres, he is a very mobile center who moves around the court very easily.