Wojnarowski wrote that "few in [Popovich's] orbit" expect him to coach the Spurs beyond the 2020 Summer Olympics.
In 2015, Popovich was named the successor to Duke head men's basketball coach Mike Krzyzewski as the head coach of the United States men's basketball national team.
Wojnarowski added that it's also possible Popovich will spend the 2019-20 season preparing for the Olympics, meaning 2018-19 could be his final season with the Spurs.
The 69-year-old Popovich has been San Antonio's head coach since 1996-97. The Spurs missed the playoffs in his first season, but Popovich has led them to 21 consecutive postseason appearances since then.
Popovich has a career regular-season record of 1,197-541, which puts him fifth all-time in wins and fourth all-time in winning percentage.
He is also a five-time NBA champion and three-time NBA Coach of the Year.
The Spurs struggled at times in 2017-18, though, as they finished just 47-35 and barely made the playoffs as the No. 7 seed in the Western Conference.
San Antonio hadn't won fewer than 50 games in a season since the lockout-shortened campaign of 1998-99.
The absence of Kawhi Leonard for all but nine games due to a quad injury played a significant role, and his future with the team is uncertainm since he can become a free agent after the 2018-19 season.
With Tim Duncan retired, Tony Parker and Manu Ginobili at the tail end of their careers and Leonard in flux, there may be no better time for Popovich to go out than over the next year or two.