For the second successive week, motorsport has been left in a state of shock following the death of MotoGP rider Marco Simoncelli.
The Italian was contesting Sunday's Malaysian MotoGP when he crashed after losing control of his Honda on the second lap.
Simoncelli slid across the track and into the path of Colin Edwards and Valentino Rossi.
The 24-year-old died as a result of his injuries.
Mark Webber wrote on Twitter: "R.I.P Marco A special talent that will be missed... Thinking of your loved ones, and all the motogp paddock... Mark."
Jenson Button also paid tribute, saying: "R.I.P Marco... Such an exciting talent lost.
"My thoughts are with his family, friends and everyone involved in MotoGP. Motorsport can be so cruel..."
Lewis Hamilton joined his fellow drivers in sending his condolences. "RIP MarcoSimoncelli. My thoughts are with his family, friends and team at this extremely sad time. Another tragic loss at such an early age."
Heikki Kovalainen wrote: "I can't believe motogp star Simoncelli has died in a crash, another great talent lost today."
Rubens Barrichello: "It was so so hard to hear the news this morning here in Brazil. The death of another great guy and great rider...RIP Simoncelli..."