Building out roster depth is a prime concern for the Spurs after committing all of their available salary-cap space to Aldridge and the returning Danny Green, with limited flexibility to pursue Indiana Pacers free agent David West and re-sign the likes of Tim Duncan and Ginobili.
Ginobili has long planned to reveal his decision about continuing his career in the La Nacion newspaper in his native Argentina. Sources say the Spurs remain quietly optimistic that Ginobili will ultimately opt for one more season.
The 37-year-old Ginobili has pondered retirement since the end of San Antonio's season, which ended with a heartbreaking loss to the Los Angeles Clippers in Game 7 of the Western Conference first round.
In 2014-15, Ginobili turned over the ball five times per 100 possessions, which registered as a career high. In the postseason series against Los Angeles, Ginobili connected on just 34.9 percent of his shots, the worst playoff field goal percentage of his career.
While Ginobili appears to be on the decline statistically, coach Gregg Popovich still wants to bring him back for a 14th season with the Spurs, as Ginobili's experience and intangibles make him an important piece as the club tries to make a run at a second championship in three years.
Ginobili had said Duncan's decision would affect whether he returned for the upcoming season. Duncan announced he would play his 19th season on Thursday.
In a column written in Spanish for La Nacion, Ginobili wrote that "Pop told us he wanted Tim and me back next season. Those words make things very difficult. Honestly, if the franchise said they didn't want me or it was time to rebuild and wanted a younger team, that would have made things very easy for me. At times, I say, 'How am I not going to play a little more?' There are other times I don't even want to see a basketball even close. I'll wait a month and see how I feel."
Ginobili has averaged 14.3 points throughout his career in the regular season and 15.2 points per game in the postseason.
Aldridge announced that he was joining the Spurs in a tweet Saturday. His deal will be a four-year maximum contract worth more than $80 million, with an opt-out after the third year, a source told Stein. He had played all nine seasons of his NBA career with the Portland Trail Blazers, making four All-Star teams.
San Antonio's odds to win the West improved to 2-1 with the news of Aldridge's signing, besting Oklahoma City and defending champion Golden State. The Spurs are 4-1 to win the NBA title, behind only Cleveland (9-4).
Sources told Stein that the signing of Aldridge all but clinches that Popovich, at the very least, will coach beyond Duncan's playing career as opposed to walking away when the future Hall of Famer finally retires, as Popovich has joked about on many occasions.
ESPN.com's Michael C. Wright contributed to this report.