Sources close to the situation told ESPN.com the Spurs came to the conclusion this week that it was best to release Jackson -- even at this unusually late date -- to try to "move forward" with the players who will be in Popovich's playoff rotation.
Popovich told local reporters Friday night before San Antonio's home game against Sacramento that it was a "tough decision because, on a personal basis, I've known (Jackson) a long time and I enjoy him very much."
"But you've got to make decisions that are tough sometimes," Popovich said, describing it as both "a basketball decision and a family decision."
Jackson had largely fallen out of San Antonio's main rotation and thus had team officials privately concerned that the 13-year veteran's "strong personality," as one source put it, would create extra locker-room tension that the Spurs don't need at a time they're already concerned about the health of stars Tony Parker and Manu Ginobili heading into the playoffs.
NBA rules stipulate that any player released after March 1 is not eligible to appear in the playoffs with another team, meaning that Jackson's season is effectively over.
He could sign with a new team after clearing waivers next week but would not be allowed to appear in the postseason with a new club.
Jackson was a member of San Antonio's title team in 2003 and was reacquired in March 2012 in a deadline-day trade with Milwaukee. He averaged 6.2 points, 2.8 rebounds and 1.5 assists in 19.5 minutes in 55 games this season.