Kolosov started the 2020–21 season with Dinamo-Molodechno of the Belarusian Extraliga. However as travel restrictions due to the COVID-19 pandemic led made the main goaltenders for Dinamo Minsk unavailable, Kolosov made his Kontinental Hockey League (KHL) debut. He had also agreed to terms with the Erie Otters of the Ontario Hockey League, a major junior league in Canada and the United States, who had selected him 22nd overall in the 2020 CHL Import Draft. Kolosov played 9 games for Dinamo during the season, and was later named to the Belarusian national team for the 2021 World Championship.