(CNN) -- Tiger Woods is dealing with a back injury and doesn't know if he'll be able to play at the Masters next month. He may not be the only multiple major winner from the U.S. struggling to be ready for Augusta.
Phil Mickelson -- a three-time Masters winner -- pulled out of the Valero Texas Open on Saturday after sustaining a pulled muscle. He got through half of his third round but then stopped.
The Golf Channel said he injured his right side.
Mickelson earlier this year skipped the Farmers Insurance Open with a back complaint.
"My back's feeling great, my body's been feeling great," Mickelson said in a statement posted on the PGA's website. "I felt as good as I have all year. My speed is back, I was hitting the ball hard, driving it great.
"I pulled a muscle on my downswing trying to hit the ball hard on the (first hole -- his 10th). It just killed and it wouldn't subside for 10 or 12 seconds.
"I'm going to go back to San Diego for a couple of days and have a doctor take a look at it but there's really not much you can do for a pulled muscle. I hope I'll be OK to play the (Shell Houston Open) but I just don't know."
Mickelson barely made the cut at the Texas Open.
"As you might imagine, he's trying to get ready for Augusta, he's hitting a lot of drivers, hitting them harder," his caddie, Jim Mackay, told the Golf Channel. "He hit one off the first tee, his 10th hole today and just felt a little pain in his side.
"It continued on for a few minutes and he just decided that he didn't want to take anything to chance relative to what's going on the next couple weeks."