SAN DIEGO -- An ailing back could cut short Phil Mickelson's stay at the Farmers Insurance Open this week.
Mickelson, who is making his 2014 PGA Tour debut at Torrey Pines after tying for second last week at a European Tour event in Abu Dhabi, United Arab Emirates, was visibly bothered by back issues following several swings on the North Course, where he closed with a birdie for a 3-under 69 that put him in a tie for 16th place.
"My back locked up on me,'' Mickelson said. "It just kind of tightened up, and I wasn't really able to start a downswing. I'll get some treatment tonight and see if I can get it to loosen up and maybe get something tomorrow before I play. And see if I can go.
"And if not, it's not the end of the world either. I don't feel like it's too far off ... it's just tight and I just couldn't swing from the top. It just kept locking up and giving me a shooting pain. I kind of flinched.''
Mickelson, 43, has been mostly free of such injuries throughout his 22-year career.
In 2010, he acknowledged that he was diagnosed with a form of arthritis, but said medication has mostly kept that issue in check.
"I just think I'm getting old and if I overdo it, it's just prone to getting a little bit tight,'' Mickelson said. "It's just a muscular thing. My back feels fine. It's just the muscle on the side.''
Mickelson managed four birdies and one bogey on the North Course, which was playing about four strokes easier than the South, where Mickelson is scheduled to play Friday.
Stewart Cink shot a 64 on the North to lead the tournament.
"I kind of milked my way around the golf course and I was able to do it on the North Course because the penalty wasn't as severe as it is on the South,'' Mickelson said. "I'm able to kind of get it up by the green, and get up and down and salvage par. Made a couple of birdies. But it won't hold up on the South Course, so I've got to get it better.''
Mickelson is scheduled to play next week's Waste Management Phoenix Open, where he is the defending champion, as well as the AT&T Pebble Beach National Pro-Am in two weeks.