The NBA is investigating the Oklahoma City Thunder for potentially violating the league’s player participation policy, sources told ESPN.

The game under NBA review is Oklahoma City’s March 7 home win over the Portland Trail Blazers in which the Thunder’s starting five of Shai Gilgeous-Alexander, Jalen Williams, Chet Holmgren, Luguentz Dort and Isaiah Hartenstein, as well as Cason Wallace, all sat out. For Gilgeous-Alexander, it was just his second missed game this season.

Without its top players, Oklahoma City beat the Blazers 107-89, led by Aaron Wiggins’ 30-point effort and Jaylin Williams’ first career triple-double.

The investigation into the Thunder continues the NBA’s move to closely monitor potentially improper absences around the league.

The Utah Jazz received a $100,000 fine earlier this week for sitting star forward Lauri Markkanen for multiple games. The NBA is also looking into the Philadelphia 76ers for the recent absences of players such as Paul George (knee, back, finger) and Tyrese Maxey (back, finger), sources said.

Unlike Oklahoma City, which at 54-12 has the best record in the Western Conference, Utah (15-52) and Philadelphia (22-44) own among the worst records in the league this season.