Fabbri tore his left ACL on Feb. 4 in a game against the Pittsburgh Penguins and had surgery a few weeks later to repair the damage in Chicago. He was cleared to play on July 31.
St. Louis had announced on Sunday that Fabbri would miss the rest of training camp.
The 21-year-old appeared in 51 games last season, scoring 11 goals and 18 assists.
The Blues selected Fabbri 21st overall in the 2014 NHL Draft.