The Spurs said Leonard's timeline for return would be determined at a later date, and the All-Star forward didn't participate in the scrimmage.
"We're still rehabbing his thigh," Spurs coach Gregg Popovich said. "And he'll probably miss the beginning of preseason or a good deal of preseason, and we're not going to put a timetable [on a return]. But he's working at it, and we'll get him back as soon as we can."
The Spurs never said when Leonard's injury occurred, but Popovich indicated the issue first developed sometime last season. San Antonio issued a statement, saying Leonard "continues a rehabilitation program for right quadriceps tendinopathy."
Leonard missed time in the 2017 playoffs due to an ankle injury suffered in Game 5 of the Western Conference semifinals against Houston, and he aggravated that sprain in Game 1 of the conference finals, forcing him to sit out the duration of San Antonio's 4-0 series loss to the Golden State Warriors.
Popovich said Leonard hasn't suffered a recent injury, adding that the forward's ankle is completely healed. Leonard said at the start of training camp that he was able to resume workouts at full capacity approximately two weeks after San Antonio's season came to a close.
"No, nothing happened," Popovich said. "It's just last year ... working on things from last year. It's gone a little more slowly than we thought. No, [the] ankle's fine."
A seventh-year veteran, Leonard averaged 25.5 points and 5.8 rebounds per game last season on the way to making his second All-Star Game, in addition to earning recognition as a first-team All-NBA player. Leonard was also named first-team All-Defense.