Vijay Singh would have entered the third round of the AT&T National just five strokes off the lead Saturday, but his back acted up and forced the Fijian to withdraw from the tournament.
Singh, who has battled back problems in the past, was slated to tee off seven groups ahead of the leaders alongside Spencer Levin.
The 48-year-old got off to a fast start on Thursday with a three-under 32 on his opening nine. Singh played his second nine in one-over par for an opening 68, which he followed with an even-par 70 in round two.
Singh, a three-time major champion, has three top-10 finishes this season, including a second-place finish at the Northern Trust Open.
In three previous appearances at the AT&T National, Singh has tied for 12th, seventh and ninth.