Krejčí was born in Strakonice, Czech Republic and played basketball for the youth academy of Sokol Pisek.

[5] Krejčí was selected with the 37th overall pick by the Washington Wizards in the 2020 NBA draft[6] and subsequently traded to the Oklahoma City Thunder.

[7] On 28 January 2021, he signed with the Oklahoma City Blue, the Thunder's NBA G League affiliate, where he rehabbed the ACL injury he sustained in Zaragoza.

He was named to the All-Star Five of the 2019 FIBA U20 European Championship Division B in Matosinhos, Portugal after averaging 14.9 points, 5.1 rebounds and 5.1 assists, leading his team to the silver medal.

In February 2019, Krejčí made his debut for the senior national team during the 2019 FIBA Basketball World Cup qualification stage.