Fernando Alonso out of Bahrain GP with rib injury following lung collapse
McLaren's Fernando Alonso has been barred from racing in the Bahrain Grand Prix after suffering "rib fractures" and a partially collapsed lung in his 180mph crash in Australia.
Medics made the call after conducting scans on the two-time world champion.
He will be replaced by McLaren reserve driver Stoffel Vandoorne, who will be making his F1 debut in Bahrain.
A "disappointed" Alonso says there was "a risk the fracture could affect the lung" and he "respects the decision".
In Thursday's news conference in Bahrain, the 34-year-old revealed he suffered a pneumothorax - a partially collapsed lung - as a result of the accident in Melbourne but this had now healed.
He said it was "not 100%" that he will be able to race in China in two weeks and he will be tested again in the next eight to 10 days after which governing body the FIA will evaluate his condition.
|Read more from the Bahrain Grand Prix|
|Qualifying decision strange - Hamilton|
|Preview feature: Sparks and sand set to fly|
|What motivated drivers' open letter to F1 bosses?|
Alonso added: "I am already recovered from the pneumothorax but the rib is too fresh and it could be a potential problem.
"I have no respiratory problems. It is a small risk, but I understand they want no risk. It is just a question of time - it should be OK in the next 10 days but there is no guarantee."
Alonso will stay in Bahrain for the race weekend to help Vandoorne and the team.
The FIA said Alonso's chest scans "showed insufficient resolution of the signs to allow him to compete".
It is the second time in just over a year that Alonso has been forced to miss a grand prix on medical grounds - he sat out the 2015 season-opener in Australia following a heavy crash in pre-season testing.
The Spaniard spent 90 minutes with FIA doctors after arriving in Bahrain on Thursday, undergoing the standard checks for any driver who has suffered a heavy crash.
Alonso's car rolled and landed upside down after he hit the back of Haas driver Esteban Gutierrez's car in Melbourne on 20 March.
His McLaren-Honda team have had to prepare a new chassis and engine for this race as a result of the extensive damage incurred in the accident.
Vandoorne, a 24-year-old Belgian, is the reigning GP2 champion - the level below F1 - and one of the most highly regarded drivers not to have a regular F1 drive.
He will fly overnight to Bahrain from Japan, where he has been testing the car he races in their Super Formula series.
Vandoorne tweeted: "About to board for Bahrain, a bit earlier than expected but so much looking forward to it. Will do my very best for the team."
He is a possibility to replace Britain's Jenson Button as Alonso's team-mate in 2017 and racing this weekend provides him an opportunity to showcase his abilities.
Former McLaren driver Kevin Magnussen, now racing for Renault, said he expected Vandoorne to be able to compete with Button.
"I think he can do that - he's well good enough to be in F1," said Magnussen, who beat Vandoorne to the 2013 Formula Renault title and was Button's team-mate in 2014. "So he will have a good race."