Last summer, the Mercedes team boss returned to the paddock wearing a sling, after badly breaking his arm in a road cycling crash.

And according to Salzburger Nachrichten, Wolff is now recovering from yet another injury, having suffered "a fall during endurance training".

The newspaper said the 43-year-old injured his knee.

Another Austrian publication, Kronen Zeitung, said Wolff even had to visit hospital, after falling from an exercise ball and breaking his knee-cap.

"His knee is like a football," a source is quoted as saying.

In the past days and weeks, Wolff's wife Susie, the Williams test driver, has posted videos on social media depicting her training with an exercise ball.