Irving had until Thursday to decide on his contract status and will now be eligible to sign a deal with any team in the league.
It's move that would force Kyrie Irving's hand in free agency, although reports have shown that the cryptic point guard has been showing plenty of interest in signing with the Brooklyn Nets.
Opting in would have led to a $21.3 million salary for Irving, but he's expected to get a whole lot more than that as an unrestricted free agent.
Of course, as Bulpett notes, Durant's achilles injury throws a wrench into this summer's free agency, with the possibility of him opting into one more year with the Golden State Warriors becoming more likely.
As Charania reports, Irving can sign with any National Basketball Association team or sign a new deal with the Celtics when free agency opens. For comparison's sake, Damian Lillard - Irving's All-NBA second-team backcourt mate this season - is slated to make $29.8 million with the Portland Trail Blazers next year.
Irving, 27, demanded a trade out of Cleveland in 2017, with Boston supposedly being one of his preferred destinations.
He appeared in 67 games last season averaging 23.8 points and a career high 6.9 assists per game. He also shot 49 percent from the field and almost 41 percent on 3-pointers.
The Celtics can offer Irving a bigger deal than anyone else this offseason, but the expectation is he'll be signing elsewhere, despite his pre-season proclamation that he would sign long-term in Boston this summer.