The Flyers announced late last month that Patrick had a second abdominal surgery before being drafted and is expected to return to full activity in four to six weeks.
At the scouting combine in early June, Patrick said he had a sports hernia on both sides and that one was "misdiagnosed." Philadelphia-based Dr. William Meyers performed the surgery.
The injury contributed to him missing more than half of last season for Brandon of the Western Hockey League.
Despite the injury, the 18-year-old Patrick scored 20 goals and 46 points in 33 games last season. Overall, the 6-foot-2, 198-pounder has 91 goals and 204 points in 160 career games and was the WHL playoff MVP in leading Brandon to the championship in 2016.
Patrick's medical issues were part of the questions about him leading up to the draft, and the Flyers' medical staff evaluated him independently.
The Associated Press contributed to this report.