Harkless' recovery could range from two to three weeks, sources said.
The Blazers announced on Tuesday that Harkless would have arthroscopic surgery to remove a loose particle in his left knee. He was scratched from that night's game against the New Orleans Pelicans with knee soreness.
Harkless is averaging 6.5 points and 2.7 rebounds in 59 games (37 starts) for Portland this season.
Information from The Associated Press contributed to this report.