'Great level of concern': Legendary coach Gregg Popovich ruled out indefinitely with undisclosed illness

After being ruled out indefinitely from the NBA season earlier this week, it's been revealed San Antonio Spurs coach Gregg Popovich suffered a "serious" health issue.

The popular coach did not travel with the team on its current road trip this week, with Mitch Johnson to serve as interim coach during Popovich’s absence.

Johnson was informed hours prior to the weekend tip-off against the Minnesota Timberwolves that the 75-year-old Popovich was unavailable because of an undisclosed illness.

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According to an ESPN report, Popovich suffered a health issue before the game against Minnesota.

"I was told it was a health issue, and it was a serious health issue that the Spurs dealt with over the weekend," Shams Charania said.

"It was a situation on Saturday night pre-game where Gregg Popovich needed medical attention in San Antonio ... There is a great level of concern around the situation for the Spurs, for Gregg Popovich..."

The Spurs have not made an official statement on the legendary coach, who is the NBA’s career leader with 1,390 victories and another 170 postseason wins while winning five NBA titles. He is in his 29th season, all with San Antonio.

“He’s not feeling well,” Johnson said. “This has happened before. I think everybody’s just always got to be ready for the next man up.

"We’ve had it with injuries and sometimes people get sick or don’t feel well or things come up in life. He’s just not feeling well.”

It marked the third time Johnson has served as head coach in Popovich’s absence.

Former assistant coaches Tim Duncan and Becky Hammon have also served as Spurs head coach because of an illness or medical procedure for Popovich in the past five seasons.