Last Updated: 31/03/14 11:00am
Phil Mickelson is the latest player to suffer a pre-Masters injury concern after withdrawing from the Valero Texas Open.
The left-hander, who was way out of contention at the time, withdrew on the second tee after pulling a muscle in his side (his oblique) when hitting a driver on the second hole - his 11th of the day - in Saturday's third round.
"I pulled a muscle on my downswing trying to hit the ball hard on the second hole. It just killed and it wouldn't subside for 10 or 12 seconds," said Mickelson in a statement.
Mickelson's caddie Jim Mackay said Mickelson's preparations for The Masters may have played a role.
"As you might imagine, he's trying to get ready for Augusta, he's hitting a lot of drivers, hitting them a little harder," said Mackay
"He just felt a little pain in his side and it continued on for a few minutes and he just decided he didn't want to take anything to chance relative to what's going on the next couple of weeks."
Mickelson is in the field for next week's Shell Houston Open before he heads to The Masters at Augusta to try and win a fourth Green Jacket.
Mickelson, who will head back home to San Diego on Monday morning to get his injury checked out, was set to pay an early visit to Augusta next week to hit some balls and play a practice round, but may now have to revise those plans.
Mackay said: "In a perfect world, he'd love to play Houston, he loves the tournament, loves the city and it's great preparation for Augusta but obviously he's going to make the right decision relative to what his body's telling him."
Five-time major champion Mickelson had birdied his last hole on Friday to make the halfway cut on the number and said after his second round two-under 70 that he was pleased with how he was hitting the ball.
"I'm hitting the ball hard, I'm hitting it high, my speed is back, my back feels great, my body feels great, and I'm able to hit the ball hard again," he said on Friday.
However, he was calling a different tune after his withdrawal on Saturday, telling the Golf Channel: "There's really not much you can do for a pulled muscle. I hope I'll be okay to play the Shell in Houston, but I just don't know."
It's the second time this year Mickelson has withdrawn in the middle of a tournament. He pulled out of Torrey Pines after making the cut because of a back injury.
While Mickelson's withdrawal looks precautionary, Tiger Woods is still unsure if he will make it to the starting line at Augusta as he continues to battle a back back which forced him to skip last week's Arnold Palmer Invitational at Bay Hill.
Woods has been plagued by back problems since last year but the 38-year-old's condition has worsened over the past month.
Australian Jason Day - the runner-up at Augusta in 2011 and also third last year - also pulled out of Bay Hill after failing to recover from a thumb injury.
Day suffered the injury during his win at the WGC-Accenture Match Play Championship and it also caused him to withdraw from the WGC-Cadillac Championship in early March.
Steven Bowditch secured his first PGA Tour win with a one-shot victory in the Valero Texas Open at TPC San Antonio.
Mickelson withdrew on the tenth hole of his third round at the Texas Open with a pulled oblique muscle. His caddie Jim 'Bones' Mackay said it was a precautionary measure
Steven Bowditch remains on course for a first PGA Tour success after a third round 68 at the Valero Texas Open.