Luke Donald's position as world number one is under threat despite the Englishman making the cut at the RBC Heritage with a two-under second round.
Donald, 34, is joint 56th, 11 shots behind American leader Colt Knost.
He needs a top eight finish in South Carolina to stay above Northern Ireland's Rory McIlroy at the top of the standings.
Three birdies in a bogey-free first seven holes helped Donald recover from an opening four-over-par 75.
He spent 40 weeks at number one before being replaced by McIlroy in March, when the US Open champion won the Honda Classic by two strokes.
Donald regained top spot two weeks later by winning a four-man play-off in the Transitions Championship in Florida.