[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.

[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.

[12] A few days after his debut, Cissoko was loaned out to Baskonia's satellite club, Iraurgi SB, in the second-tier LEB Oro.

[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.

In his debut, Cissoko played for 4 minutes and recorded no stats other than 1 turnover as the Spurs suffered a 25-point loss to the Los Angeles Clippers (99 - 124).

[28][29] In his regular season debut with the Austin Spurs on December 28, 2023, Cissoko recorded 22 points, 9 rebounds, 2 assists and 2 steals in a 118 - 117 victory over the South Bay Lakers.

[31] On February 5, 2025, Cissoko, along with two second-round draft picks (2028, 2029), was traded to the Washington Wizards in exchange for center Jonas Valančiūnas,[32] but was waived the next day.