[2] Krejčí made his professional debut for Zbrojovka Brno in its home match against Sparta Prague on 2 October 2016, which ended in a 3–3 draw.
[5] In July 2022, he became Sparta's captain, replacing Bořek Dočkal who had retired the previous season.
[10] In May that year, he helped the club to win its second championship title in two seasons,[11] and domestic cup as captain.
[13] In March 2022, Krejčí received his first Czech senior call-up from coach Jaroslav Šilhavý.
[14] In the UEFA Euro 2024 qualifying match on 24 March 2023, Krejčí scored his first goal on his international debut against Poland which is considered to be the fastest in the Czech Republic national football team history.