St Johnstone defender Liam Gordon faces four to six weeks out after fracturing an elbow in training.
The 23-year-old made 17 appearances last season.
Manager Tommy Wright told the club's official website: "This is obviously hugely disappointing news both for the team and for Liam. He finished last season strongly and has started pre-season very well ahead of the 2019-20 campaign.
"The injury came from an innocent fall during training this morning and it's just an extremely unfortunate thing to have happened."