Cissoko's father, Yaya (or Yakia), was a basketball player who represented Senegal at the 1980 Summer OlympicsinMoscow.[2] Growing up in France, Sidy played basketball from a young age and looked up to Kyrie Irving, seeing as he was shorter than the rest of his teammates at the time.[3] He reached the under-15 level with CTC Center Essonne.[4]
In 2017, at 13 years of age, Cissoko moved to Spain and joined the youth ranks of Baskonia.[5][6]In2020–21, Cissoko played with the Baskonia reserves in the fourth-tier Liga EBA and averaged a team-leading 17.4 points per game.[7][8] He also led the Baskonia junior (under-18) team to a fourth-place finish in the junior national championship while leading the competition in points and assists.[5]
Cissoko was called up to the Baskonia first team ahead of the 2021–22 ACB season.[9] On September 26, 2021, Cissoko made his senior debut for Baskonia at the age of 17, playing 28 seconds in a 72–61 loss to Joventut Badalona.[10][11] This allowed Baskonia to retain his European rights.[12]
A few days after his debut, Cissoko was loaned out to Baskonia's satellite club, Iraurgi SB, in the second-tier LEB Oro.[13] He averaged 10.8 points, 3.0 rebounds and 2.4 assists in 32 games played.[12][13] Cissoko trained with the Baskonia first team as well; he later said he learned a lot from watching Wade Baldwin IV.[3]
Cissoko was invited to play in the 2022 Nike Hoop SummitinPortland, Oregon, recording three points, seven rebounds, four assists and three steals in 23 minutes for the World Team in a 102–80 loss to Team USA.[5][14]
On July 19, 2022, it was announced that Cissoko had signed with the NBA G League Ignite, a developmental team affiliated with the NBA G League.[15] Cissoko became the first European player to sign with the Ignite.[12] He pointed to the success of 2022 lottery pick, Dyson Daniels, who played at the NBA Global Academy in Australia before spending the 2021–22 season with the Ignite.[15] At the time of his signing, Cissoko was ranked as the third-best European prospect in his class by Jonathan Givony of ESPN, behind countrymen Victor Wembanyama and Rayan Rupert.[15]
Cissoko was one of four Ignite players chosen to compete in the Rising Stars Challenge at the 2023 NBA All-Star Weekend, recording one rebound, one assist and one steal for Team Jason in a 40–32 loss to Team Joakim.[16][17] He was also one of 24 players named to the G League's inaugural Next Up Game.[18]
On January 16, 2023, Cissoko scored a then-season-high 21 points in a 141–119 defeat to the Fort Wayne Mad Ants.[19] In another loss to the Mad Ants the following day, he scored 20 points on 8-of-10 shooting, including 4-of-5 from three.[20] Cissoko had five straight games of 20 or more points in February and March.[21] This included a season-high 24-point performance, along with six rebounds and four assists, in a 123–97 loss to the Memphis Hustle on February 24.[22] Cissoko tied his season high with 24 points against the Sioux Falls Skyforce on March 15.[23]
On March 29, 2023, Cissoko announced he was entering his name in the 2023 NBA draft.[3]