David Robinson said he has completed his purchase of a 1.88-percent share of the franchise from former Spurs president and chief executive officer Jack Diller.
"All the I's are dotted and the T's are crossed," Robinson said. "I think we're in."
The Spurs' other investors had to give their approval for the sale to become official. The NBA's board of governors does not have to vote on the transfer because the share is less than 5 percent.
Though Robinson's stake could be worth more than $5 million based on media valuations of the Spurs and the recent sale of other NBA franchises, he said he did not join the ownership group hoping to make money. Forbes magazine listed the Spurs' worth in February at $283 million, eighth-highest in the NBA and up 24 percent from a year ago.
"I just want to learn what (being an owner) is about," Robinson said. "I want to get a feel for how things work. After not playing last year, this sort of makes me feel part of the team again."