The statement said that the procedure was a "recognised, occasional consequence of open heart surgery", and carried a low risk. It would keep Mr Clinton, 58, confined to bed for three to 10 days.

"The scar tissue developed as a result of fluid and inflammation causing compression and collapse of the lower lobe of the left lung," his office said. "The surgery will be done either through a small incision or with a video-assisted thoracoscope inserted between ribs."

Doctors discovered the condition during a recent routine x-ray.

The operation will take place tomorrow at the New York-Presbyterian hospital, where Mr Clinton had open heart surgery after some of his arteries had been found to be more than 90% blocked.

The former president said he planned to stick to a scheduled round of golf in Florida today with George Bush senior for tsunami relief. "I feel fine," Mr Clinton told reporters after a visit to the Oval Office with the former president. "And we're going to go play golf tomorrow."

Though he would return to work as soon as possible, he added: "I'm going to slow down for the next couple of weeks. But I'm in good shape."

He has lost a lot of weight since chest pains led him to be checked by doctors last year. They found lesions that needed surgery. His appetite for junk food and Southern soul food were deemed partly to blame, and he has been on a strict diet over the past six months. Other than that, Mr Clinton has had the normal health problems that often accompany ageing, such as periods of slightly elevated cholesterol and hearing loss. In 1997, he was fitted with hearing aids.

In early 2001, shortly after his presidency ended, he had a cancerous growth removed from his back; it turned out to be basal cell carcinoma, the most treatable form of skin cancer.

In 1996, he had had a pre-cancerous lesion removed from his nose, and a year before that had a benign cyst taken off his chest.