The 20-year-old Holmgren appeared to have suffered the injury last Saturday while participating in a pro-am game in Seattle which featured NBA stars LeBron James, Jayson Tatum and first overall pick Paolo Banchero, among others.
“Certainly, we are disappointed for Chet, especially given the excitement he had about getting on the floor with his teammates this season,” Thunder general manager Sam Presti said in a statement.
“We know Chet has a long career ahead of him within our organization and the Oklahoma City community.
“One of the things that most impressed us during the process of selecting Chet was his determination and focus.
“We expect that same tenacity will carry him through this period of time as we work together and support him during his rehabilitation.”
It comes after Holmgren impressed during this year’s Summer League — an off-season competition in which teams predominately play rookies, second year and fringe NBA players to give minutes to developing talents and see who fits and who doesn’t.
In one particular victory over the Utah Jazz earlier this summer, Holmgren wowed the fans in his 24 minutes on the court, setting records as he went.
The big man finished with 23 points — including 4-of-6 attempts from three-point range — seven rebounds and four assists.
He also finished with six blocks, the most ever in an NBA Summer League game.