The Houston Rockets remain uncertain when Russell Westbrook will return from injury as the NBA All-Star guard sat out Tuesday's Western Conference first-round series opener against the Oklahoma City Thunder.

Westbrook's status for the Rockets-Thunder playoffs matchup was already up in the air due to the 2017 MVP's strained right quadriceps.

The nine-time All-Star sat out the final seeding game against the Philadelphia 76ers, having missed the loss to the Indiana Pacers prior to the postseason starting in Orlando, Florida.

Asked about Westbrook prior to Game 1 against the Thunder at Walt Disney World Resort, Rockets head coach Mike D'Antoni said: "Can't rule anything out, but don't rule anything in."

Westbrook, who posted 20 points, six assists and five rebounds in the Rockets' defeat against the San Antonio Spurs earlier this month, had previously felt discomfort in his right quad.

He sat out back-to-back games after feeling soreness during a loss to the Portland Trail Blazers on August 4.

A blockbuster acquisition from the Thunder, Westbrook has been averaging 27.2 points, 7.9 rebounds and 7.0 assists per game.

The Rockets – seeded fourth in the Western Conference – are eyeing their third NBA championship and first since 1995.