Paul Casey is out of next week's Dubai World Championship, the event which could have seen him crowned as the European Tour's number one this season.

England's world number five has taken advice not to risk further injury to the shoulder muscle he tore in practice for The Open in July.

Casey spent nearly three months on the sidelines before returning at the Volvo World Match Play Championship a fortnight ago, but then withdrew early in the final round of last week's HSBC Champions tournament in Shanghai.

The 32-year-old, who lies fifth on the "Race to Dubai" money list, flew from China to the United States for an MRI scan in the hope that he would be given the all-clear to compete in the Middle East.

But manager Guy Kinnings said: "Paul will not play sadly.

"His intercostal muscle is not torn again, but it is inflamed and he cannot risk it in Dubai."

Casey will now seek further opinion before making a decision on when he will be fit enough to return.

Next week's event is for the leading 60 money-winners on the circuit, but the field will now be only 58 as American Anthony Kim, runner-up to England's Ross Fisher at the Match Play in Spain, has decided not to play.

Casey is still in line for an Order of Merit bonus that could be in excess of £316,000.

At the 1996 Volvo Masters Australian Robert Allenby, having fractured his sternum in a car crash the previous month, struck an opening drive 30 yards and then quit.

The rules at the time required him to do that so he could collect a bonus of around £60,000 - he then gave it to charity - but things are different now.

A note in the European Tour members' handbook states: "To be eligible for bonus pool prize money a player must participate in the Dubai World Championship unless he has a mitigating circumstance."

It says further on that a player withdrawing "for reasons of injury, serious disability or personal emergency which is deemed acceptable by the Chief Executive (in his absolute determination) will remain eligible to receive any applicable bonus pool payment."

Tour boss George O'Grady has confirmed that Casey clearly meets the requirement.

The sum would be just over £316,000 if Casey remains fifth on the "Race to Dubai" standings, but even if he drops to 15th - that is how far the pool extends - he would receive more than £113,000.

Whoever wins the money list race earns over £900,000 and that could be in addition to the £750,000 first prize at the tournament itself.

It was to have been even more, but the economic situation brought a 25% reduction in both purses.

The first half of this year was the best of Casey's career. He won in Abu Dhabi, reached the final of the Accenture Match Play in Arizona, broke his US Tour duck at the Houston Open and then captured Europe's flagship BMW PGA title at Wentworth.

That lifted him to third in the world, but then came the injury as he worked on his swing with American coach Peter Kostis.

Just three years ago Casey was battling with Padraig Harrington for the Order of Merit title, but was struck by food poisoning at the final event.

Twenty-year-old Rory McIlroy is now favourite to win this season's race. A 65 today took him into third place at the Hong Kong Open and with current money list leader Lee Westwood down in 33rd place the Northern Irishman has a golden opportunity to take a sizeable advantage to Dubai.

German Martin Kaymer is third and Fisher fourth. Both took this week off, but will still have a chance of the number one spot even if McIlroy wins on Sunday.