Leonard has only played in two of the Clippers' seven games this NBA season upon returning from an ACL injury from the 2021 playoffs that saw him miss the entire 2021-22 campaign.
The two-time NBA Finals MVP has been struggling with stiffness in his surgically-repaired right knee and has missed his side's last four games.
Leonard will miss another two, having been ruled out of road games against the Houston Rockets (Wednesday) and the San Antonio Spurs (Friday) and his status is uncertain for Sunday's game against the Utah Jazz.
"He's frustrated," Lue said. "He wants to be out on the floor. To then not be on the floor, then now he can't travel, he wants to travel but obviously, that's not the right thing to do right now.
"The stiffness and what he's going through, just frustrated putting in all the work the last 15 months, and to get to this point, and not being where he wants to be right now physically.
"He's getting better, and that's the most important thing."
In Leonard's two games this season, he played both off the bench, putting in 21 minutes on both occasions, averaging 12.5 points, 6.5 rebounds and 2.0 assists. The Clippers are 3-4 this season.