Having already played at senior level on loan at second-tier HC Stadion Litoměřice during the 2019–20 season, he made his Czech Extraliga debut with Brno aged 16 on 18 February 2020, scoring the opening goal of the game against Mountfield HK of Hradec Králové[2] (he became the joint-fourth youngest scorer in the league's history – future NHL man Pavel Zacha first found the net at exactly the same age in 2013).
He was a first-round pick by the Charlottetown Islanders of the Quebec Major Junior Hockey League in the 2020 CHL Import Draft, but due to complications of the pandemic he did not move to Canada at that point,[4] instead he remained with Brno and made 23 regular season appearances in the 2020–21 Czech Extraliga season, though only provided one assist, and had a short loan with SK Horácká Slavia Třebíč.
[1] The Phoenix advanced to the playoffs semi-finals but were eliminated by the Halifax Mooseheads despite winning the first two games of the series on the road.
He again represented the Czech Republic at the 2023 World Junior Ice Hockey Championships[14] where he recorded one goal and six assists in seven games and won a silver medal (he was named his team's MVP in the overtime loss to Canada).
[1] His father Kamil Brabenec was a professional ice hockey player who made 15 international appearances for the Czech Republic and played domestically for teams including Kometa Brno, as well as for clubs in Sweden, Slovakia and Italy.