The two sides had agreed in principle on the deal Sunday.
According to one league official, the NBA has been waiting to get all the necessary paperwork from the Clippers, Celtics and Rivers’ representatives. The official still expects the Rivers deal to be completed by Tuesday.
Rivers was going to be paid $7 million per season over three years with the Clippers.
The Celtics had called a press conference earlier Monday at their practice facility outside Boston, but it was canceled and there was no timetable for it to be rescheduled.Rivers, 51, coached Boston the past nine seasons and led them to a championship in 2008 and to the NBA Finals in 2010 — both Finals were against the Lakers.