Michael Schumacher will make his planned Formula One comeback only if he gets the green light from doctors, his spokeswoman Sabine Kehm reiterated on Wednesday.
The seven-times world championship Schumacher is set to drive a Ferrari car again as long as Felipe Massa recovers from head injuries sustained on July 25 in a crash in qualifying for the Hungarian Grand Prix.
"Michael is working hard for his comeback but it was clear from the outset that this pends on the outcome of the medical examinations," Kehm told the DPA.
Johannes Peil, whose team at the Bad Neuheim sports clinic has treated Schumacher for the last nine years, had also said on the weekend that Schumacher will only race again if he passes the medicals.
"We will only know if he can drive when all the tests have been concluded," Peil told dpa.
Schumacher, 40, is working with Bad Nauheim doctors as he aims to race again three years after retirement, on August 23 at the European Grand Prix in Valencia, Spain.
Ferrari announced last week on Wednesday that Schumacher is to take the place of Massa, a move which has generated huge excitement in the motorsport world.
It is not known exactly when the doctors will make their final assessment, but it is believed to come next week.
While Schumacher's fitness is seen as no serious obstacle despite his long absence, a neck injury sustained in February in a motorcycle incident is of some concern because neck muscles are subject to extreme pressure during F1 races.
Schumacher said on his website on Tuesday that he had slight neck problems after first tests in an old Ferrari model.
"We have to get a grip on that as health has priority - that's the clear arrangement made with Ferrari and, by the way, with my wife, too," Schumacher said.
But Schumacher also said: "It's on! I accepted the challenge. And as you all know, I really love challenges."