Joe Riley has been ruled out for the season after sustaining a ruptured anterior cruciate ligament injury.
The young full-back, who made four appearances during pre-season, suffered the setback in training and will be sidelined for at least nine months.
Riley will undergo surgery this evening and City boss Gary Bowyer insists he is in the best possible hands to make a full recovery.
The City boss said: "We were waiting for full information, after he picked up the injury late last week, and it turns out his season is probably over.
"He will have an operation tonight. It is a huge shame for Joe, first and foremost, and a massive blow for the club.
"The poor lad was devastated last Thursday but came back in the day after and showed a fantastic attitude towards his recovery since.
"It was just an innocuous slip in training. We are all wishing Joe the best and will give him all the help we can. He is determined to get back as quickly as possible.
"It is important we involve Joe as much as we can while he is out and keep his spirits as high as possible, as with all the other lads we have missing at the moment."
Meanwhile, Bowyer has moved to update supporters on City's other absentees - with Jake Reeves, Paudie O'Connor and Shay McCartan yet to feature.
Bowyer added: "We cannot really put any sort of timescale on Jake, but he is doing well.
"He has been doing some ball work, which is a massive step in the right direction.
"Jake has been in high spirits around the training ground and is another great person to have around the building.
"Paudie has trained all week and looked very sharp. He provides healthy competition for a backline which performed very well against Cambridge.
"Shay trained terrifically, this morning, and should not be too far away from a return.
"Zeli has been back out on the grass today. Jermaine Anderson has trained well all week and Hope Akpan joined back in today, too."