Phil Mickelson has pulled out of the Texas Open with a muscle strain and could be a doubt for the Masters in less than two weeks time.
The three-time Augusta winner pulled a muscle in his side after 11 holes of his third round but wasn't in contention at the time.
Mickelson has now joined a list of players, including Tiger Woods, who are injury doubts for the Masters at Augusta which starts on 10 April.
"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 about his injury.
The 43-year old has had a slow start to the season as he prepares for The Masters. In eight starts he has failed to finish in the top 10 and a back injury had forced him to miss Torrey Pines in February.
In the hope of playing more competitive rounds, Mickelson entered the Texas Open for the first time since 1992 and was planning to enter this week's Houston Open.
He told 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."
Mickelson's caddie Jim Mackay admitted that five-time major winner's preparations for The Masters may have been his downfall.
"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 headed home to San Diego on Monday to get his injury examined as he hopes he will have a chance to win his fourth Green Jacket.
But original plans of playing at Houston and then an early visit to Augusta next week to play a practice round may have to be revised.
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."
While Mickelson is still hopeful of making to the starting line at Augusta, Tiger Woods remains a genuine doubt. The world number one continues to battle with his back problem which forced him out of last week's Arnold Palmer Invitational at Bay Hill.
The 38-year old has been suffering with back problems since last year and his condition is not improving with The Masters fast approaching.
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