According to ESPN's Zach Lowe, Danny Ainge may have offered a package involving Boston's best future draft picks in an attempt to acquire San Antonio's Kawhi Leonard.
The draft picks mentioned were most likely the Kings, Grizzlies and Clippers picks that the Celtics acquired from the three teams.
The Spurs apparently rejected Boston's pick-heavy offer in favor of trading for the Raptors DeMar DeRozan. This what ESPN's Zach Lowe had to say on his Podcast (per basketball.realgm.com):
"Rebuilding was just not going to be an option there," said Zach Lowe on his podcast.