2010-11: Robby Fabbri skated for the Mississauga Rebels bantam AAA team that captured the Ontario Hockey Federation championship.
2011-12: Fabbri appeared in two junior A games with the OJHL’s Toronto Junior Canadiens and was team captain of the Mississauga Rebels midget minor AAA team. He had 3 assists in a regular season game and was scoreless in an OJHL playoff contest with the Junior Canadiens. Fabbri scored 57 goals with 48 assists and had 75 penalty minutes in 60 games for the Rebels. Mississauga captured the championship of the 2012 OHL Cup and Fabbri scored 4 goals with 4 assists and 8 penalty minutes in seven games at the tournament. He was selected by Guelph in the first round (sixth overall) of the 2012 OHL Priority Draft.