Leonard had played in two triumphs to start the 2026-27 campaign but was benched for Sunday's loss to Minnesota due to the swelling.
"Forward Kawhi Leonard will undergo a treatment and rehabilitation program to address swelling in his left knee," the team said in a statement.
"Medical imaging revealed no acute injury, and Leonard will be reevaluated in one week."
Leonard, 35, had already coped with severe right knee injuries in the 2021 and 2023 NBA playoffs.
The Raptors obtained Leonard, who sparked Toronto to the 2019 NBA title, in an offseason trade with the Los Angeles Clippers that was not completed until after a resolution was reached in the Clippers' salary cap circumvention scandal.
Last month, Leonard signed a two-year contract extension worth $115 million with the Raptors.
"It's always frustrating missing time," Leonard posted on social media. "I came back to compete with this team and I'm focused on getting back to 100.
"Toronto, I've appreciated the love since I've been back. Returning soon."