Los Angeles played without Leonard in their 129-124 loss to the Milwaukee Bucks on Wednesday due to what they called "load management (knee)", but coach Doc Rivers said before the defeat there were no concerns about his fitness.
While the NBA had no issue with the decision to sit the three-time All-Star against the Bucks, the Clippers were handed a $50,000 fine for Rivers' comments.
In a release confirming the sanction ahead of the Clippers' game against the Portland Trail Blazers on Thursday, the league revealed Leonard was suffering from "an ongoing injury to the patella tendon in his left knee".
"It was shocking, but it doesn't matter to me. I'm not a guy that reads the media anyway," Leonard, who had 27 points and 13 rebounds in a 107-101 victory over Portland, said of the content in the NBA's statement.
"We're gonna manage it the best way we can to keep me healthy and that's the most important thing moving forward."
On the fine, he added: "That's just disappointing. It feels like they want players to play if they're not ready. But it is what it is.
"Like I said, I don't read into it. I've gotta do what's gonna make me healthy and what's gonna help the team be successful, and that's me being able to play basketball for us.
"That's not what the doctor's subscribing right now [playing in back-to-backs]. That's all I can say about it. We're gonna manage it and just keep moving forward."
The Clippers improved to 6-3 for the season by beating the Trail Blazers at Staples Center, claiming Rivers' 900th win as a coach in the process.