Roy had an MRI exam on his right knee after the team returned to Portland Sunday night. The Oregonian, citing an unnamed team source, reported that Roy has a bone contusion.
In text messages to ESPN.com, Roy confirmed he will not play Monday, but said a final diagnosis has not been made because a radiologist was unavailable to look at the MRI results.
The Trail Blazers play their final game of the regular season Wednesday against the Golden State Warriors.
Portland has clinched a postseason berth and will begin the playoffs on the road, either Saturday or Sunday. Roy hopes to be available for the playoffs and said for now the plan for his knee is to "rest and let it calm down, and in a couple days see where I'm at."
Roy injured the knee when his legs tangled with Lakers forward Ron Artest in the first quarter of Portland's 91-88 win.
"My foot got caught and my knee kept going," Roy told reporters afterward. He played for slightly more than a minute in the second quarter before leaving the game for good.
"I was trying to go out there because we were trying to fight for a higher seed," he said. "But I was like, 'Let me just pass it, I don't feel like I can move.' "
Roy is the Blazers' leading scorer at 21.8 points per game. He struggled with a sore back in recent days, missing practice to rest up for the playoffs.
J.A. Adande is a columnist for ESPN.com. The Associated Press contributed to this story.