Spanish Moto2 rider Luis Salom has died at the age of 24 after crashing during a free practice session at the Catalunya Grand Prix.
SAG Team rider Salom was taken to hospital and underwent surgery after the crash at turn 12 on Friday.
"It is with great sadness that we have to report the passing of Luis Salom," MotoGP said in a statement.
"Despite the best efforts of the trauma team, he passed away at 16:55 local time."
British MotoGP rider Scott Redding wrote on Twitter: "My love and heart is with Luis Salom and his family. We lost another great rider. RIP Luis."
Spanish Formula 1 driver Fernando Alonso wrote: "Such terrible news. Such anger and sadness. Rest in peace, rider. A huge embrace to Luis Salom's friends and family."
Danny Kent, the British Moto3 world champion wrote: "RIP Luis Salom, such a sad day. You'll be missed. Love to you and family."
Spanish tennis player Rafael Nadal, winner of 14 Grand Slam titles, wrote: "Very sad news. Although words can't bring comfort in times like this, all my support goes to Luis Salom's family and friends."
British MotoGP rider Cal Crutchlow wrote: "So saddened of what happened today in Barcelona."
Following a meeting of its Safety Commission, MotoGP said Sunday's race at the Circuit de Catalunya will still go ahead, but with a revised track configuration.