Sergachev played just three games in the National Hockey League, and thus Montreal will not burn the first year of his entry-level contract.
The 18-year-old was selected ninth over by Montreal in the 2016 draft and impressed enough in training camp to get a three-game look with the big club.
“Not every 18-year-old player has the chance to play with Shea Weber,” Sergachev told reporters.
Sergechev leaves the NHL without a point and had been a frequent healthy scratch.
The Russian native will continue to develop and see plenty of ice time with Windsor, for whom he scored 17 goals and 57 points as an OHL rookie in 2015-16.
“He has a good attitude. He’s a good kid,” Canadiens GM Marc Bergevin told reporters. “It will help him to play another year in the junior ranks, for sure.”
Teenage rookies must play 10 games at the NHL level for their entry-level contract to take effect.