The Raptors announced that Valanciunas has a fractured fourth metacarpal in his non-shooting hand. The fourth-year veteran will undergo further tests before the Raptors determine how long he will be sidelined.
Valanciunas scored three points in 18 minutes Friday before suffering the injury on a foul by Kobe Bryant under Toronto's basket in the final minute of the first half.
Valanciunas broke the same bone -- in his right hand -- during his 2012-13 rookie season and missed 18 games.
"It's unfortunate, and we're definitely going to miss him because of what we do, so it's next man up right now," Raptors point guard Kyle Lowry said.
Valanciunas, 23, is Toronto's third-leading scorer and leading rebounder, averaging 12.7 points and 9.3 rebounds in 14 games this season. Bismack Biyombo started the second half at center for the Raptors on Friday and could be in line for more minutes while Valanciunas is out.
Information from The Associated Press was used in this report.