Game 2 of the best-of-seven series will be played Tuesday night at Crypto.com Arena.
Asked if his best player could miss more than one game, Lue said he wasn't sure when Leonard would be able to play.
"I'm not sure," Lue said. "Like I said, he's making progress. He's been on the court the last couple days and we're not sure. We're evaluating day by day."
Leonard was unable to do any contact drills last week as the Clippers prepared for the Mavericks game with four days of practice.
Lue was asked if the medical staff has given the organization a clear indication if Leonard will be able to do contact work this week.
"We haven't gotten that far yet," he said.
Leonard has missed the last eight regular season games due to a knee issue. He last played on March 31 against Charlotte.
Leonard has played 68 games this season, the most since playing 74 games for San Antonio in 2016-17.
"It's hard for him," Lue said. "But he's getting better. He's making progress. He's been on the court the last couple days. We'll see. But he's frustrated, as he should be. Working as hard as he did this year, playing as many games, doing what he did this year and now missing Game 1 of the playoffs.
"It's tough for him, but he's 100%. We're ready to go."
