Mickelson gets treatment from physiotherapist Jim Weathers

Phil Mickelson is an injury concern for next month's US Open after pulling out of the Memorial Tournament in Ohio with a wrist problem.

The left-handed American withdrew after 11 holes of his opening round because of problems with his left wrist.

"I don't think it's anything serious - it just got worse. I couldn't grab the club and I couldn't swing," he said.

Tiger Woods shot a first round of 70 to lie five strokes behind leaders Sean O'Hair, Rod Pampling and Nick O'Hern.

South African Ernie Els is among five players a shot behind the leading trio after his opening round of 66.

Ian Poulter is the leading Briton on two under par after his round of 70, which inlcluded six birdies.

"I'll take a couple of days off, see if I can ice it and get it ready for the (US) Open," said Mickelson, who was playing the Jack Nicklaus-hosted tournament for the first time since 2002, as was Woods.

"I'll try to even play in Memphis next week if I can, but the Open is more what we're gearing up for."

The world number two was two over par at the time after a double bogey at the par-three 8th and a bogey at the par-five 11th.

Masters champion Zach Johnson also withdrew from the event, quitting after 15 holes with a sore throat.