Fabbri originally tore his ACL on Feb. 4 last season and underwent surgery in Chicago to repair the damage. After months of intense rehab that was well-documented on stlouisblues.com in August, Fabbri was medically cleared in July and joined the team on the ice in mid-September for the start of training camp.

Last Friday, Fabbri played in his first preseason game, where he recorded three shots on goal against the Washington Capitals. He played 19 minutes and 8 seconds in the game, which ranked second among all Blues forwards.

Blues General Manager Doug Armstrong said after the game against Washington, Fabbri noticed some swelling in his left knee, which caught the attention of the team's medical staff. Fabbri had an MRI on Sunday morning, and doctors felt they saw a tear in the ACL. On Monday, Fabbri flew to Chicago to see Dr. Bernard Bach, who performed the original surgery on Feb. 28. Dr. Bach confirmed the ACL tear.

Video: Fabbri injury press conference

"In a situation like this, everyone is looking for a villain, everybody is looking for why it happened. Unfortunately this is an ice hockey injury," Armstrong said. "Robby is in that uncomfortable three percent of players that had a reoccurrence of this injury."

"These last couple of days have been very difficult and pretty emotional for me and my family after finding out my season was over," Fabbri said during a press conference at Scottrade Center on Thursday morning. "I knew with my injury, there was a three percent chance of it happening again, and unfortunately I fell in that three percent… There's nothing I can do now but try to stay positive, be supportive of the guys for this season and get ready for next season."

Armstrong said Fabbri is expected to undergo surgery to repair the injury sometime within the first two weeks of October. He is expected to make a full recovery and is projected to participate in training camp when it begins next September, but he has been ruled out to play at any point this season or posteason.

"For me right now, obviously I feel terrible for Robby," Blues Head Coach Mike Yeo said. "He's a great player, he's a kid that brings a lot of life and energy to the rink every day and loves to play the game. To have that taken from him this year after going through what he did, that's disappointing. We'll do everything we can from our staff's standpoint as coaches to keep him engaged, try to keep him involved. We'll keep his head in the game here."

Video: Yeo discusses losing Fabbri for the season

"He's 21 years old, he's now going to miss a year and a half of ice hockey, and what we have to do now is focus on the positive," Armstrong added. "That is he's only 21 years old and a world-renowned doctor is going to perform the surgery. He understands the importance of rehab, he's now been though that part once. He's going to have to go back in and have laser focus on preparing for next season."

It's been a difficult training camp for the Blues. Forward Zach Sanford dislocated his shoulder during his first practice session and is expected to be out five to six months, Alexander Steen sustained a hand injury that will keep him out at least through the rest of the preseason, and defenseman Jay Bouwmeester incurred a fractured ankle during a training camp scrimmage and is expected to re-evaluated next week.

The Blues were already without Patrik Berglund, who will be sidelined until December as he recovers from a shoulder injury sustained during his offseason training program.

The rash of injuries will almost certainly create more opportunity for some of the Blues' top prospects that still remain on the club's training camp roster. Sam Blais, Tage Thompson, Klim Kostin and Wade Megan are just a few of the club's forward prospects that have impressed thus far in training camp.

Armstrong said he would "explore all options" to find ways to compensate for Fabbri's loss.

"We've sustained some injuries, but that's the sport," Armstrong said. "We're going to have to find a way to overcome it. We're going to count on these young players. I don't want to say it's a concern, but it's the next injury, when they start to multiply, it's - where is our depth after that? We're not going to make a bad trade, we're not going to overpay to do something, we're not in a vulnerable situation. But we do have to explore different avenues."