The ailment was initially listed as a "left shoulder strain" on the team's injury report for Sunday's game against Portland. Popovich said Leonard was hurt during Friday night's game against the Suns.
"It’s too bad," Popovich added. "He was starting to get back into form a little bit after playing a couple of games."
The full scope of Leonard's recovery timeline is currently unclear, though the Spurs are reportedly hopeful he can play as early as Thursday against the Lakers, per ESPN's Michael C. Wright.
The perennial MVP candidate's 2017-18 campaign has been marred by injuries to date. Leonard only made his season debut on Dec. 12 after recovering from an offseason quad injury, which was unrelated to the lingering ankle injuries that ultimately ended his 2016-17 season in the third round of the playoffs.
Leonard had shown signs of his old self to start January, recording back-to-back 20-plus-point outings in wins over the Knicks and Suns. In eight appearances this season overall, the 26-year-old has averaged 15.9 points, 4.3 rebounds, 2.1 assists, and 1.8 steals per game.