Sedláček played in the Sparta Prague youth academy until 2018, where he moved to Dutch club AZ, initially joining the reserve team Jong AZ competing in the second-tier Eerste Divisie.[3] He made his league debut for Jong AZ on 5 October 2018, replacing Tijjani Reijnders in the 73rd minute in a 2–2 home draw against Helmond Sport.[4]
VVV-Venlo
On 31 January 2022, Sedláček signed a one-and-a-half-year contract with Eerste Divisie club VVV-Venlo, joining the club alongside Jong AZ teammate Sem Dirks.[5][6] He made his debut on 4 February 2022, starting in a 5–0 away win over MVV in the Eerste Divisie.[7] Exactly one month later, on 4 March, Sedláček was forced off due to an injury after ten minutes of play in the league game against Volendam;[8] it was later confirmed how he would miss the remainder of the 2021–22 season, as he had torn his ankle ligament.[9]
The following season, Sedláček was mainly a starter for VVV, making 34 total appearances in which he failed to score.[10] On 5 January 2023, he had signed a new contract with the club, keeping him in Venlo until 2025.[11]
On 24 November 2023, Sedláček scored his first competitive goal for VVV in a 2–1 league loss to Cambuur.[12]
On 19 August 2024, Sedláček's contract with VVV was terminated by mutual consent.[13]
Teplice
On 27 August 2024, Sedláček returned to his youth club Teplice.[14]
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