Paul Casey's hopes of finishing the season as European number one have suffered another big blow.

The world number four, who because of a rib muscle injury has not played since the first week of August, is out of next week's Alfred Dunhill Links Championship in Scotland.

And Casey, second to injured German Martin Kaymer on the Tour money list, will not be back in action now until the Volvo World Match Play in Spain at the end of next month.

"While I feel I am extremely close to being fully fit I have decided to heed advice and withdraw from the Alfred Dunhill Links Championship," he said.

"I am really disappointed as it is a fantastic event and one I am very sorry to miss, but I know that coming back too soon could undo all the rehabilitation work I have done.

"It has been a very frustrating time, but I feel my patience is being rewarded having now completed several light practice sessions with no ill effects.

"I am looking forward to building on this over the next few weeks to get my game in shape for my return.

"My first event back will now be the Volvo World Match Play Championship where I hope I can get my Race to Dubai campaign back on track."

Casey suffered a tear of the internal oblique muscle at the 10th and 11th rib and an intercostal strain in the same area while practising for The Open in July.

He tried to return at the Bridgestone world championship, but pulled out after a few holes and then withdrew from the US PGA Championship and the start of the FedEx Cup play-off series in the States.

Kaymer is currently out of action after needing surgery when he broke toes in a go-karting accident a month ago.

He is targeting a return at the Castello Masters in Spain on October 22-25 - the week before the Match Play.

Their lay-offs have opened the door to Rory McIlroy, Lee Westwood and Ross Fisher to take over at the top of the standings next week.