On 31 March 2020, Nzosa signed a five-year contract with Unicaja of the
Liga ACB after
FIBA Europe ruled in favor of the club in its dispute with Stella Azzurra. The deal included a clause of about €1 million to allow him to leave for the
National Basketball Association and the
EuroLeague. In the 2020–21 season, Nzosa joined Unicaja's senior team and immediately became a key player. On 27 September, at 16 years and 10 months of age, he made his Liga ACB debut. In 18 minutes, he recorded 10 points, shooting 5-of-5 from the field, three rebounds and two blocks in an 81–78 win over
Andorra. He joined
Ricky Rubio and
Luka Dončić as the only 16-year-olds in league history to score at least 10 points in a game, while becoming the second-youngest debutant in team history behind Pablo Sánchez. Two days later, Nzosa made his
EuroCup debut, going scoreless in nine minutes in a 96–88 win over
Metropolitans 92. On 3 October, he scored 10 points on 4-of-4 shooting in a 90–86 loss to
Manresa, becoming the first under-18 player to score 10 or more points in their first two ACB games. On 11 October, Nzosa recorded four rebounds, four blocks, three assists, three steals and two points in a 71–66 victory over
Valencia. He surpassed
Kristaps Porziņģis as the youngest player in league history with least four blocks in a game. On 9 March 2021, Nzosa posted a season-high 16 points and four blocks in a 98–89 loss to
AS Monaco. He was named to the
ACB All-Young Players Team. From April 2021, Nzosa was sidelined for five months with
athletic pubalgia and was cleared to play by September. His play declined in the
2021–22 season, and he fell from a potential top-five pick to a late-second-round selection in the
2022 NBA draft, according to draft projections. He was selected with the 54th overall pick by the
Washington Wizards, while remaining under contract with Unicaja. For the 2022–23 season, Nzosa was
loaned to
Real Betis Baloncesto. On 29 August 2024, Nzosa signed with
Carplus Fuenlabrada of the
Primera FEB on loan from Unicaja. ==Personal life==