Orlando Magic forward Jonathan Isaac suffered a torn anterior cruciate ligament in Sunday's 132-116 win over the Sacramento Kings.
Isaac dropped to the floor after driving between two defenders and was treated on court before being wheeled away accompanied by Magic president of basketball operations Jeff Weltman.
In a statement released on Sunday, Magic confirmed an MRI scan showed the 22-year-old had torn the ACL in his left knee.
"Isaac will be out indefinitely and his return to the court will depend on how he responds to treatment and rehabilitation," the statement said.
Isaac had only recently recovered from a knee injury sustained on January 1 against the Washington Wizards, when he landed awkwardly and was diagnosed with a "posterior lateral corner injury and medial bone contusion".
It was expected he would miss the remainder of the season, but the delay caused by the coronavirus pandemic gave him the chance to recover in time for the restart in Orlando.
"That was tough, man," team-mate Aaron Gordon said, the Magic bench having been clearly downcast despite their resounding victory.
"That one brought me to tears, and instantly, just because I know how good of a guy J.I. is and how hard he works and how hard he has worked to get back since hurting himself in D.C. That was tough."