De Angelis was airlifted to Dokkyo hospital in Mibu, Japan, on Saturday after a heavy crash midway through a practice session before qualifying.
He suffered three broken ribs and five fractured vertebrae as well as a head injury and lung contusion and has spent the last six days in intensive care.
The team, citing Clinica Mobile doctor Michele Zasa, said the 31-year-old from San Marino had not suffered brain or serious spinal damage but still needed assistance breathing.
"The situation that concerns the (lung) contusion is the most delicate," Zasa said.
"The next two or three days will be important to verify the stability of his breathing and to assess the situation according to pulmonary therapies in place."
A separate medical official with MotoGP said De Angelis was still not fit to be transferred to a Europe hospital.
"But we hope to have his condition stationary for the next days and then are ready to transfer him," the official said at the Phillip Island circuit where riders were preparing for Sunday's Australian Grand Prix.
De Angelis's seat will be taken by Australian rider Damian Cudlin, who returns to MotoGP two years after his last race with Paul Bird Motorsport in 2013.
The 30-year-old Cudlin will also race at the Malaysian Grand Prix in De Angelis's stead at Sepang next week.
Championship leader Valentino Rossi said he had spoken to De Angelis since his crash and criticised the Motegi track for having "dangerous" sections.
Monster Yamaha Tech 3 rider Pol Espargaro also suffered a crash at Motegi and hit his head on a barrier but escaped unharmed.
Riders would discuss whether changes were needed at Motegi at a safety commission meeting on Friday, Autosport.com said.
Italian great Rossi is bidding for his seventh premier class victory at Phillip Island as he bids to maintain his championship lead over Yamaha team mate Jorge Lorenzo.
(Reporting by Ian Ransom; Editing by Peter Rutherford)
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