Roy also missed Friday's game against Orlando.
Roy left during the third quarter of the Blazers' 120-108 victory over the Milwaukee Bucks on Wednesday night. An MRI on Thursday confirmed the strain.
The two-time All-Star leads Portland with 23.4 points and 5.1 assists per game.
Jerryd Bayless started for Roy again.
Information from The Associated Press was used in this report.