Mašín was rated as a top prospect[1] who was ranked 18th on the NHL Central Scouting Bureau's mid-term ranking of International skaters,[2] rising to the 10th spot with the release of their final rankings in April 2014.[3] He was selected by the Tampa Bay Lightning in the second round (35th overall) of the 2014 NHL Entry Draft.
During the 2013-14 season, Mašín was the Czech U20's most penalized player with 102 penalty minutes.[4]
Professional
On 13 October 2015, the Lightning signed Mašín to a three-year, entry-level contract.[5]
He made his professional debut with the Syracuse Crunch on 9 April 2016 following the conclusion of his junior season. In four games with the Crunch at the end of the 2015-16 AHL season, he posted zero points and a +1 rating.
Following his fifth season with the Syracuse Crunch, Mašín placed 6th in all-time in games played with the Crunch, with 58 points and 303 penalty minutes in 273 games.
On 1 July 2020, a report surfaced that Mašín would sign as a restricted free agent from the Lightning with Russian club, Amur Khabarovsk of the Kontinental Hockey League (KHL).[6] It was later confirmed by the club on 7 August 2020.[7]
In his second season with Amur in 2021–22, Mašín went scoreless in 15 regular season games before leaving the club and transferring for the remainder of the year to Finnish club, Ilves of the Liiga, on 14 October 2021.[8]
On June 23, 2022, Mašín secured a one-year contract extension to continue with Ilves in the 2022–23 season.[9]