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Marquez sustained an injury to his optic nerve when he crashed at the start of free practice at Sepang a fortnight ago. He attempted to continue with the Malaysian Grand Prix weekend before ultimately pulling out after qualifying.
The Spaniard remained in doubt for Valencia, announcing earlier this week that he did not expect to be fit to race but would attend the event in case his condition improved. But as first practice got underway this morning, Marquez announced that he would be sitting the weekend out.
With Bradl 23 points ahead of Marquez and no other riders in mathematical contention, the German therfore becomes Moto2's second champion.
Bradl had dominated the first part of the season - with four wins in the opening six races giving him a 62-point championship lead.
But then reigning 125cc champion Marquez hit form, taking seven victories and grabbing the points lead at Motegi.
Marquez's season then went downhill - penalised for crashing into Ratthapark Willairot after the chequered flag at Phillip Island, he surged from last on the grid to third in the race but could not prevent Bradl reclaiming the championship advantage, and then had his season-ending crash in Malaysia.
The Spaniard recently announced that despite suggestions Honda and Repsol would fast-track him into MotoGP for 2012, he will remain in Moto2 for next season.
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