Ailing Spurs coach Popovich reportedly out indefinitely
The San Antonio Express-News, citing a league source, said the 75-year-old coach is "OK" and "just needs to rest."
Johnson had taken over for Popovich on Saturday about two and a half hours before the Spurs' home victory over the Minnesota Timberwolves.
"He's not feeling well," Johnson told reporters at the weekend. "This has happened before. I think everybody's just always got to be ready for the next man up... He's just not feeling well."
Popovich had been in charge when the Spurs beat the Utah Jazz in Salt Lake City on Thursday.
The Spurs are scheduled to play the Clippers in Los Angeles on Monday and the Rockets in Houston on Wednesday before hosting Portland on Thursday.
Popovich is the NBA's all-time leader in victories for a coach with 1,390 regular-season wins and another 170 post-season triumphs.
He has guided the Spurs to five NBA titles in his 29 seasons at the helm.