The team signed the 18-year-old Toronto native to a three-year deal over the summer. He saw action in four preseason games with Phoenix.
Domi played in 21 postseason games last year with the Knights, helping lead them to their second-straight OHL Championship. The 5-foot-10 forward was drafted by the Coyotes with the 12th overall pick in the 2013 NHL Entry Draft.
Domi's move to the OHL leaves 24 players on the Coyotes' roster. They start the season Oct. 3 at home against the New York Rangers.