Forsbrand was taken to hospital with a temperature of 103F. After chest X-rays, he was put on a course of antibiotics and eventually allowed to return to his hotel at about 1am. The 34-year-old shot rounds of 83 and 78 on the first two days of the pounds 1.6m championship and was lying last of the 20 players.
His temperature was reported to have dropped yesterday, but he was told to stay in bed all day. Forsbrand's withdrawal - he will still receive the last-place prize money of pounds 37,000 - left the Open champion John Daly to play with a marker.
Daly opened with two rounds of 80 and, at 18-over-par, was 23 strokes behind the half-way leaders Fred Couples, Vijay Singh and Wayne Riley.
Fred Couples shrugged off the discomfort of a stiff back to charge into a three-way tie for the lead after the second round of the $2.3m Johnnie Walker World Championship on Friday.
Couples, the 1992 Masters champion, saved the best for last as he birdied four of the final five holes for a four-under-par 67, the day's lowest round, in a testing breeze on the Tryall course. "As I tightened up, I started hitting the ball much better. I don't know why," said Couples, who joined Fiji's Vijay Singh (68) and first-round leader Wayne Riley (71) on a five-under-par 137.
They were three strokes clear of the American Loren Roberts (70). Nobody else in the 20-man field was under par.
"The five years I have been coming here I have putted well and that helps," said Couples, who is as familiar with these greens as anyone in the field.
His back stiffened on the range as he was warming up for the round, but physiotherapy helped temporarily. "Early on it felt great, and when I started making all those birdies it stiffened up. I can't say what's wrong."
Couples earned a share of the lead when Singh and Riley, playing together in the final pairing, both bogeyed the final hole.
"I made some nice putts, but missed some short ones," said the Fijian- Indian Singh, who was the favourite among the local galleries. He eagled the par-five 17th, but then missed a short putt to drop a shot at the last. Twenty-four shots separated the strung-out field after a day in which only five players broke par.
The defending champion Ernie Els blamed poor thinking for his dismal showing. "I am losing my head out there," said a frustrated Els, who was tied for third to last after shooting two-over-par 73 to stand a distant 15 strokes behind the leaders. "I am losing my head out there," said a frustrated Els, who was tied for third to last after shooting two-over- par 73 to stand 15 strokes behind the leaders. "I am not enjoying it the way I should be," last year's US Open champion said.