(Reuters) - Phil Mickelson has a special relationship with the Farmers Insurance Open which is played in his native San Diego but he was considering withdrawing from the event after nursing a troublesome back in Thursday's opening round.
The American repeatedly winced at the top of his backswing as he carded a three-under-par 69 on the North Course at Torrey Pines and said his ultimate decision on whether to pull out would depend on how he responded to treatment.
"I'll work on it tonight and tomorrow and we'll see how it goes," left-hander Mickelson, a three-times winner of the PGA Tour event, told reporters after mixing four birdies with a lone bogey to end the round five strokes off the pace.
"It's the start of the season so I don't want to do anything stupid here. I don't think it's anything serious, I just couldn't go after it today. If I can get it to feel better for tomorrow, I can go and maybe shoot a good round.
"Hopefully it will work out. If not, it's not the end of the world and I'll take a few days off and rest it up, but either way we'll see how it goes."
Asked whether he had considered pulling out of the event on Thursday, Mickelson replied: "Never thought about not starting, but around the turn I thought about maybe taking this week off and seeing if I could get it a little bit better.
"I've never had any back problems. It's more of a muscular thing. It's just locking up when I try to start on the downswing. I don't know. I'll get some treatment and see if it will go away. It might take a few days' rest. We'll see."
Mickelson, who tied for second at the European Tour's Abu Dhabi Championship on Sunday in his first tournament of the year, was thankful to play his opening round at Torrey Pines on the easier North Course, one of two layouts hosting the event.
"I was fortunate I was on the North course so that I could manage around and kind of half-swing it around it and get up and down and make some pars," the 43-year-old added.
"But it wasn't the best day for me. I'll have to get it better for tomorrow because (on) the South Course you can't get away with that kind of effort."
The brutal South Course played almost four strokes harder than the North in Thursday's opening round and Mickelson is well aware of the challenge facing him if he tees off in Friday's second round.
"I'm hopeful I can play, but I don't want to do anything stupid here the first week of the year, or second week for me of the year," he said.
"I want to make sure that I'm healthy and I that don't get into bad swing habits just because I've having a bit of tightening.
"(Today) I had to kind of ease into everything so that it wouldn't lock up. I could do that on the North, I can't do that on the South."
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by John O'Brien)