2008-09: Lukas Sedlak scored 12 goals with 17 assists and 14 PMs in 44 games for Ceske Budejovice's U18 team in his native Czech Republic. He was scoreless in four playoff games with 4 PMs.
2009-10: Sedlak made his Czech junior debut in fine form, putting up 4 goals and 8 assists in 11 games for the Ceske Budejovice U20 club. Sedlak was the leading scorer for Budejovice's U18 team, scoring 29 goals with 27 assists in 37 games and finishing with 76 PMs. He represented the Czech Republic at the 2010 U17 World Hockey Challenge and had 1 goal with 1 assist in five games.
2010-11: Sedlak played a full season with Ceske Budejovice's U20 team and was an assistant captain for the Czech Republic team at the 2011 U18 World Junior Championship. He notched 14 goals and 13 assists in 47 games for Budejovice and was the second leading goal-scorer with 3 goals in five games for the Czech Republic at the junior tournament. He also had an assist and was -3 on a team that finished eighth in the ten-team tournament. Sedlak was selected by Chicoutimi in the first round (14th overall) of the 2011 CHL Import Draft.
2011-12: Sedlak put up 45 points with the QMJHL’s Chicoutimi Sagueneens, favoring the assist column with 28. In the playoffs he had a much smaller impact with only eight points in 18 games and a -3 rating. Like he has since he was 16, he appeared in a lot of international tournaments, but for first time was a non-factor. He set up one goal in 16 international games and finished the tournaments with a combined plus/minus of -6.
2012-13: Sedlak returned to Chicoutimi for his second QMJHL season and was a team captain for the Czech Republic at the 2013 World Junior Championship. He scored 15 goals with 19 assists for the Sagueneens and was +1 with 64 penalty minutes in 48 regular season games. Chicoutimi was fifth in the East Division and lost to Quebec in a six-game first round playoff series. Sedlak scored 1 goal with 4 assists and was +1 with 8 penalty minutes in the series. He scored 1 goal with 2 assists and was +1 with 10 penalty minutes in six games for the Czech U20 team in Ufa. The Czech Republic defeated Switzerland 5-4 in the fifth-place game. Sedlak signed a three-year entry-level contract with the Blue Jackets in April, 2013.
Sedlak is the kind of player who is not going to get the recognition for how well he plays. He does all the little things right, but besides a strong shot does not bring too much more of significance to the table. He plays well in his own zone, but has room to improve on the offensive side of the game.
Following the end of last season, Sedlak agreed to an entry-level, three-year deal with the Blue Jackets. He will make his professional debut with Springfield this season.