Regazzoni funeral scheduled for Thursday

Police are still trying to determine the exact cause of the car crash in which the former Grand Prix winner died last week.

Autopsy tests are still ongoing amid suggestions that he may have suffered a stroke or heart attack prior to the accident, rather than being killed in the impact with a truck.

Regazzoni's death has resulted in an outpouring of emotion from many of his former rivals, who were all shocked at his passing.

Niki Lauda told Gazzetta dello Sport: "I remember many episodes, all of them beautiful. When I got to Ferrari he was the idol, and for me he continued being so later on as well, because to my eyes he was the best combination between a professional race driver and a playboy.

"He was never scared, even when he got into some very heavy accidents. He looked indestructible. Always smiling, I liked him because he always thought positively."

Emerson Fittipaldi added: "I'm so sorry about Clay's passing. I've always been a friend of his; we felt united in our passion for racing.

"Regazzoni was a special person, someone who had a lot of courage after the accident in Long Beach.

"I remember many episodes with him and they are all nice. Many of them have to do with my home by the sea in Brazil, where drivers from my time would always come a week before the GP.

"Clay was phenomenal at tennis. We had great, happy games with him."

Alex Zanardi said: "There's not much to say when things like this happen, but this is very sad and touches me deeply.

"It also demonstrates that normal roads are risky, maybe even more than when you drive in a race on Sunday afternoon.

"It's absurd that someone like Clay, who's done whatnot in his life, should lose his life in a road car accident. It's so strange and absurd."

Even team boss Flavio Briatore, who only entered F1 long after Regazzoni's career had come to an end, said he was saddened by the news.

"He always lived his dramas inside a car," said the Renault chief. "First the accident on the track, now the one that took away his life. It was an incredible destiny.

"I felt very affectionate to him, he always supported me and supported F1."