Gun jockey Silvestre de Sousa is in a race against time to be fit to ride at Sha Tin on Sunday after suffering a back injury at Happy Valley on Wednesday night.

The star Brazilian, who has racked up an incredible 40 wins in his stint so far, pulled up noticeably sore on the Richard Gibson-trained Mr Darthvegar in the night’s fourth race.

Stewards have since revealed De Sousa suffered soft tissue damage in the incident, which saw him immediately taken to hospital after dismounting from the horse while still on the track.

“The chief medical officer has advised the stewards that MRI tests have revealed soft tissue damage to the lower back for which jockey De Sousa is now being treated,” licensing committee secretary Steve Railton said in a statement.

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“The chief medical officer also advised that, depending on De Sousa’s response to this ongoing treatment, the injury may resolve in sufficient time for him to fulfil his riding engagements at the Sha Tin race meeting on Sunday, March 10.”

De Sousa was fresh off a win on Wednesday night after he booted home the Tony Millard-trained Gift Of Lifeline in the third race.

De Sousa has a full book of 11 rides on Sunday and will be desperate to be fit for the meeting having secured the ride on Dubai hopefuls Wishful Thinker and Elusive State.

He will also ride the highly rated Simply Brilliant and last-start winners Cordyceps and Prance Dragon.

Meanwhile, the full list of international jockeys booked to ride in next week’s BMW Hong Kong Derby has been released.

James McDonald, Oisin Murphy, Craig Williams, Hugh Bowman and Ryan Moore will jet in for the premier four-year-old race.

While Bowman rode Furore to victory in the Classic Mile, the other internationals will ride in this year’s four-year-old series for the first time.

New Zealander McDonald will ride the David Hall-trained Ho Ho Khan, Murphy will ride European import Gold Chest for Richard Gibson and Australian Williams has been booked for the Chris So Wai-yin-trained Tianchi Monster.

Master trainer John Size revealed previously that Englishman Moore had been secured to ride Enrichment.