Iverson left the team just before the All-Star break, missing five games, and also withdrew as a participant in the All-Star Game, because his daughter was ill. After returning to the team, he played three games before taking the leave the team announced Monday.
Sixers President and General Manager Ed Stefanski made the announcement.
"At this time, we feel that it is in the best interest of the Sixers, Allen and his family that he be allowed to deal with a very serious issue that is far greater than the game of basketball," Stefanski said.
Iverson -- who signed a one-year deal with the Sixers in December after leaving the Memphis Grizzlies -- will miss at least the next three games and may miss more, the Sixers said.
Iverson, 34, is averaging 13.9 points in 25 games with Philadelphia this season.