McLaren's Fernando Alonso has revealed he suffered fractured ribs and a collapsed lung in his frightening crash in Melbourne 10 days ago, and admits he cannot guarantee he will be cleared to race in China in two weeks' time.

Alonso says he was determined to compete this weekend in Bahrain, but with his ribs not fully healed doctors deemed it too risky for him to take part. And while the Spaniard insists such risks are 'very small', he concedes he cannot say decisively when he will be eligible to return.

"To summarize a little, last week I was okay Sunday - some knee pain but not big things. I had the green light to leave the track and everything was okay," Alonso explained in Thursday's official FIA press conference in Bahrain.

"On Monday I had a bit of overall pain, nothing too serious. Then I flew back, arrived in Spain and the pain was a little more, so we did a proper check and I had a small pneumothorax on the lung.

"We took advice from the doctors to relax at home and repeat the scan last Monday - the pneumothorax is gone more or less but I had some rib fractures. And because F1 is a very unique position in the car, and with the g-forces, there was a risk the fractures could move into the lung.

"It's not like broken leg or arm where you can deal with the pain; it's the chest where there are organs, so we cannot do much more."

Asked whether he was confident of racing in China, Alonso added: "It is not 100 percent - it will be another test I need to do in the next eight or 10 days and after that the FIA will evaluate again, as they did today.

"I will recover. I am already recovered from the pneumothorax, it’s just the ribs are not ‘glued’ let’s say, so it could be a problem. It is a very, very small risk, but I understand we all want zero risk. So it is just a matter of time. In the next 10 days it should be fine but we cannot guarantee - maybe five days, maybe 10, maybe 12."

Alonso said he made the personal choice to stay in Bahrain in order to aid his replacement Stoffel Vandoorne, and also to assist McLaren as thanks for the team's work in preparing his car - which suffered extensive damage in the crash - in time for the weekend.

"The team did a fantastic job preparing the car so I wanted to try [to race] until the last moment," Alonso said. "Now I stay here all weekend to help Stoffel because it is a good opportunity for him, and to help the team because I love what I do, I love F1 and racing.

"I want to learn from the outside how the team prepare, the actions around qualifying, the strategy, the pit stops - I want to get involved in everything on the outside because it could help me on the inside next time."