Rondo is scheduled to have surgery as soon as possible to repair a torn anterior cruciate ligament and chances are he will not be ready for the start of the 2013-14 season.
A clear timetable for his return will not be available until the surgery has been performed on an injury he first suffered against Atlanta on Friday - it was then termed as a hyperextension.
Rondo reported to the Fleet Center for Sunday's afternoon clash with the Miami Heat for the pre-game shoot around but was taken off to hospital after complaining of pain in his knee.
The seventh season guard was voted to the Eastern Conference's All-Star starting team, but Commissioner David Stern will now choose a replacement for him.
Even with Rondo in the line-up the Celtics went into the Heat game on a six-game losing streak and they face the prospect of missing out on the play-offs for the first time since the 2006-7 season.
But that run did come to an end in exciting fashion with a 100-98 win in double overtime despite 34 points from Miami's LeBron James.
Boston rallied from a four-point deficit in the final period to force overtime and Paul Pierce put them in front with a three-pointer in the second extra period, with Shane Battier missing from deep just before the buzzer that would have won the game for the Heat.