"The MRI taken earlier did not show anything significant," Portland general manager Rich Cho told the team's website (www.nba.com/blazers).
"However, a more thorough review from our team physician did reveal a partial tear."
The 36-year-old Camby, the team's leading rebounder, became the fifth Portland player to need knee surgery this season.
Camby is averaging 5.9 points, 11.3 rebounds, 2.3 assists and 1.87 blocks in 39 games, all starts.
He was injured in Monday's 113-102 victory over Minnesota. No date has been set for the surgery or his return.
(Reporting by Gene Cherry in Salvo, North Carolina. Editing by Steve Ginsburg)