The 25-year-old - who is one of only seven Narodak players in this summer's squad to also be involved at Euro 2020 - has enjoyed a stellar campaign in the Eredivisie with FC Twente in 2023-24.
Finishing third in the Dutch top-flight standings, the Tukkers achieved their highest league placement in a decade, securing a spot in the qualification rounds for next term's revamped Champions League.
Unlike a number of Czech internationals who ply their trade away from their homeland, such as Bayer Leverkusen duo Patrik Schick and Adam Hlozek, Sadlier is a regular fixture for his club side, starting 31 league games this campaign.
Since making his debut for Narodak in the early part of 2019, the midfielder has earned 24 caps for his country, finding the net once.
Czech Republic's Sadilek out of Euro 2024 after bike accident
Following a hectic weekend for Sadilek in the Czech Republic camp, his chances of featuring in a second major tournament have been dashed by a freak injury.
After Friday's 7-1 thrashing of Malta in a warm-up game, Narodak players who featured for more than 45 minutes were spared of footballing action the next day, instead taking part in individual training programs.
For Sadilek, this recovery day included a period of cycling, in which the 25-year-old fell and "suffered a laceration in the leg area", leaving him unavailable for selection for the remainder of the international window.
Head coach Ivan Hosek has spoken of his frustration after one of his key midfielders picked up a freak injury, whilst also providing his condolences to the player at a difficult time.
"It is a big weakness for us, because Michal (Sadilek) is one of the experienced players," Czech boss Hasek hold the team's official website on Sunday morning.
"After all, he also put on the captain's armband during the match against Malta. On behalf of the whole team, I wish him a speedy recovery."
Czech Republic's midfield dilemma
With just over a week to go before a Euro 2024 opener with Cristiano Ronaldo's Portugal in Leipzig, Czech Republic have seen their midfield plans blown apart by an unlikely injury.
As stated by Hasek, the Twente enforcer captained his nation in the thrashing of European minnows Malta on Friday and had a good chance of starting in a midfield double pivot alongside West Ham United's Tomas Soucek.
Sadilek's absence is likely to weaken Czech Republic's protection of their three centre-backs in a 3-5-2 formation, a system which helped Hasek's troops to conceded just six goals across eight qualifying matches for the tournament.
For now, Narodak are down to just 25 players as they prepare to fly to Germany this week, with Hasek set to decide whether to call-up a replacement "in the near future".