In July 2017, Saiz signed his first professional contract with
Real Madrid, terminating previously with Estudiantes. One month later, he was loaned to
San Pablo Burgos, debutant in the Spanish
Liga ACB, where he averaged 9.1 points and 4.9 rebounds per game. In July 2018, he was loaned to
Iberostar Tenerife of the Liga ACB. He will make his debut in European competition as the Canarian team is qualified for the
Basketball Champions League. On August 1, 2019, Saiz signed with
Sun Rockers Shibuya of the
B.League. On June 4, 2020, Saiz signed with
Chiba Jets of the B.League. On June 10, 2021, Saiz signed with
Alvark Tokyo of the B.League. On June 21, 2022, he re-signed with Alvark Tokyo. On June 14, 2023, he re-signed with Alvark Tokyo. On June 12, 2024, he re-signed with Alvark Tokyo. ==International career==