Some Olympic and Paralympic teams are not bringing any doctors to treat their athletes should anything go wrong during the Games.
Doctors from 141 nations out of a possible 203 have registered to practice in the UK during the competition, figures from the General Medical Council (GMC) suggest.
The GMC, which oversees all doctor registrations, said that 849 foreign doctors had applied for temporary registrations, and it was processing a further 29 applications.
The French team has registered 58 doctors, the highest number for any country, to support their 333 athletes.
Brazil has registered 50 doctors for 259 athletes, and the United States have registered 46 doctors for 530 athletes.
Eighteen doctors will be supporting Team GB's 542 sports men and women.
Some countries such as Iraq, Saudi Arabia, Nepal, Zambia and Honduras have registered one doctor each.
The doctors are registered temporarily and can only treat non-UK nationals for the duration of the Games.
The GMC has rejected 40 applications, including one by Mexico for a vet and another by Venezuela for a masseuse - neither of which need to be registered with the GMC.
GMC chief executive Niall Dickson said: "Doctors play a vital role at all levels in all sports and of course at the highest level their contribution is critical.
"London 2012 is a great national occasion and we are proud to have played our small part by enabling overseas doctors to come here and support their Olympic athletes during the Games."