[5] On 15 August 2015, hmade his first team debut with jersey number 32 in the second round of the Eredivisie 2015/16 against Willem II, ending in a 3–0 victory.

Coach Frank de Boer sent him onto the pitch in the 77th minute, replacing Riechedly Bazoer (Ajax had both of their wingers injured, German Amin Younes and Dane Viktor Fischer).

[3] Five days later on 20 August, Černý made his European competition debut in a home play-off match of the 2015/16 UEFA Europa League against Czech team FK Jablonec (a 1–0 victory for Ajax, entering the pitch in the 85th minute, replacing Anwar El Ghazi).

[7] In October 2017, Černý did not finish a Wednesday match in the Dutch Cup against third-tier De Dijk, in which he contributed one goal to a 4–1 victory and progression to the Round of 16.

[8] Subsequent examinations confirmed that he tore the anterior cruciate ligament in his knee during the cup match, ending his season prematurely.

[22] In 17 competitive matches during the season, Černý scored six goals and provided seven assists, earning his first call-up to the senior national team.

[22][23] In early July 2021, Černý transferred from Utrecht to Twente permanently, signing a two-year contract with an option for another two years.

[citation needed] Černý started the 2022–23 season in great form, having scored five goals in nine matches by early September.

In mid-May, the team from Enschede achieved a significant 4–0 victory against Nijmegen, with Černý scoring the opening goal, assisting two more, and receiving applause from fans upon substitution.

This call-up drew media attention as if Černý played in the against Latvia or Malta in early September, he would become the youngest player to represent the team.

[41] On 17 November 2022, Černý scored his first goal in a UEFA Euro 2024 qualifying match against Faroe Islands, ending in a 5–0 victory for the Czech Republic.