LONDON, Penn. -- His wife's continuing battle with cancer has led to Darren Clarke pulling out of the next two PGA Tour events -- the WGC-American Express World Championship in San Francisco starting on Thursday and the Michelin Championship in Las Vegas.

"My mind's not on the job for obvious reasons," said Clarke, whose appearance at last week's Dunhill Links Championship in Scotland was his first in more than a month.

The Ulsterman was also out for a month when his wife Heather was taken to the hospital during the BMW Championship in May after suffering heart problems as a reaction to the drugs she was taking following chemotherapy.

Clarke might now decide to play in the Madrid Open on Oct. 13-16 instead so he can return home quickly if necessary.

Andrew Chandler, his manager, already has spoken to PGA Tour Commissioner Tim Finchem about the fact that the Ryder Cup star will not now complete the minimum 15 events required for membership there.

He has played 12 so far, and was originally hoping that on top of the next two weeks he would qualify for the season-ending Tour Championship to complete his quota.

"We'll be asking for a medical extension to his membership now," stated Chandler.

The Dunhill Links was Clarke's 12th European Tour event of the season.