With the Masters looming in less than two weeks, Phil Mickelson pulled out of Saturday's third round of the US PGA Tour's Texas Open with a pulled muscle.

Mickelson was one-over for the day after three bogeys and two birdies when he withdrew at the par-five second hole, his 11th of the round.

He said he felt the injury when teeing off at the first, his 10th hole of the day.

"I pulled a muscle on my downswing trying to hit the ball hard on the first hole," Mickelson said. "It just killed ... and it wouldn't subside for 10 or 12 seconds."

He went on to par the hole, but with the first major tournament of the year starting at Augusta National on April 10, Mickelson opted to play it safe and withdraw.

Mickelson, whose five major titles include three Masters green jackets, has had a slow start this season.

A back problem forced him out of Torrey Pines in February, and he hasn't had a top-10 finish in eight starts including this week.

He entered the Texas Open for the first time since 1992 in a bid to play more competitive rounds before the Masters.

He birdied his last hole on Friday to make the halfway cut on the number and said he was pleased with how he was hitting the ball.

On Saturday, he said in his statement that this latest setback came out of the blue.

"My back is feeling great, my body has been feeling great. I felt as good as I have all year," he said.

"My speed is back, I was hitting the ball hard, driving it great."

Mickelson said he didn't yet know if he would be able to go ahead with plans to play in next week's Houston Open, which he won in 2011.

"I am going to go back to San Diego for a couple of days and have a doctor take a look at it, but there is really not much you can do for a pulled muscle," he said.

"I hope I will be OK to play in Houston but I just don't know."

Mickelson isn't the only marquee player fighting to get fit for Augusta.

World No 1 Tiger Woods is receiving treatment for back spasms and said on Monday he wasn't sure if he would be ready to play at Augusta.

(China Daily 03/31/2014 page23)