The NBA is investigating why Philadelphia center Joel Embiid did not play in the team’s nationally televised season opener against Milwaukee.

The league confirmed the investigation on Thursday. It was opened as part of the NBA’s player participation policy that went into effect last season.

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NBA’s Player Participation Policy Triggers Investigation

Such a move was to be expected. The NBA has said that any time a star player misses a game — it defines “star” as someone who was an All-Star or All-NBA selection in any of the previous three seasons, and Embiid is one of those — an investigation can be opened to “promote compliance” with league rules and can include “independent medical review and related determinations regarding player availability.”

Embiid’s Injury History and Recent Olympic Success

Embiid — who helped the U.S. win Olympic gold at the Paris Games — missed the entire preseason and was ruled out for Wednesday’s opener against Milwaukee with the 76ers citing “left knee injury management.” Embiid has a long history of injury issues, including knee problems.

Embiid has never played more than 68 games in a season and was limited to 39 last season in large part because of knee surgery.

NBA Investigation Timeline and Additional Player Absence

It is not clear how long the investigation will take. Philadelphia was also without Paul George for Wednesday’s game; he suffered a bone bruise during the preseason.