The injury occurred early last week during a pickup game at Chase Center. Green last week told Andscape's Marc Spears on Saturday that he expects to miss four to six weeks.
"I dodged a bullet and learned that today by the way it's [positively] reacting," Green told Spears. "Even with an MRI you don't see the trend of it immediately. The swelling is down."
Green will meet with reporters on Monday at the Warriors' media day. Training camp will begin the following day, with Golden State's first preseason game set for Oct. 7. The Warriors open their regular season on Oct. 24 against the Phoenix Suns.
The 33-year-old Green is entering his 12th season in the NBA with a new four-year, $100 million contract extension under his belt. Last season, Green played in 73 games, working through a number of nagging injuries, including to his back, neck, foot and knee. Two seasons ago, he missed one month because of a back injury.