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Nicky Hayden has been ruled out of the Czech Grand Prix after being knocked out in a qualifying crash at Indianapolis.

Hayden, 31, was absent from the race at the Brickyard but had hoped to be able to compete at Brno this weekend.

But Hayden, who also sustained a hand injury, is now expecting to return at next month's San Marino Grand Prix.

"It's tough to miss another race," he said. "The doctors told me racing was a bad idea and my team agreed."

Pramac Ducati rider Hector Barbera will also miss out after his run of bad luck continued.

The Spaniard returned from a broken leg at Indianapolis but crashed out in practice and broke several vertebrae in his back.

He will again be replaced by Toni Elias at Brno.