Gregg Popovich reportedly suffered a "health issue" over the weekend before the Spurs game ... with the legendary head coach being ruled out for an "indefinite period."
Shams Charania broke the news Monday morning, saying the 75-year-old coach suffered the issue prior to the Spurs matchup against the Timberwolves on Saturday ... which they won, 113-103.
Assistant coach Mitch Johnson -- who stepped in for his boss and will now serve as interim coach -- said at the time the all-time winningest coach in league history was "not feeling well.