A source said that Green is seeing another specialist Tuesday to receive confirmation.
Green suffered the injury during Thursday's preseason win over the Toronto Raptors in Japan. It was initially believed to be a sprain, but further examinations after the Rockets returned to Houston revealed the fracture.
Green, 33, has averaged 10.2 points in 20.9 minutes per game off the Rockets' bench over the past two seasons. His injury is a significant blow to Houston's second unit.