Roy came out during the third quarter of the Blazers' 120-108 victory over the Milwaukee Bucks on Wednesday night. He had an MRI Thursday morning which confirmed the strain.
The two-time All-Star leads the Blazers with 23.4 points and 5.1 assists per game.
The injury-depleted Blazers have had to lean on Roy, who is in his fourth NBA season.
Jerryd Bayless was tapped to start in Roy's place Friday night against the Magic.
Information from the Associated Press was used in this report