US Open:Briton David Howell, who has struggled for fitness over the past 12 months, withdrew from the U.S. Open on Monday because of a wrist injury.

The 31-year-old, who pulled out of last month's PGA Championship at Wentworth because of a long-standing back problem, has been replaced by American Luke List, the second alternate.

Howell, forced to withdraw from his last three events on the PGA Tour, said he had initially sprained his wrist while practising in England eight days ago.

"It was fairly innocuous and I didn't think I'd done anything damaging," he told reporters.

"So I hung around and didn't hit any balls at all until yesterday.

"I played nine holes here and it felt worse. We did a couple of tests this morning with (physiotherapist) Dale (Richardson) and it probably deteriorated a little from yesterday. So that's it I'm afraid."

Howell led the race for last year's European Tour order of merit crown for much of the season before slipping back into third place after a painful right shoulder affected him for his last seven tournaments.

The four-times European Tour winner felt he overstretched himself during his 2006 campaign and had planned to cut down on his playing schedule this year.

The U.S. Open, being staged at Oakmont Country Club for a record eighth time, starts on Thursday.