'I have never been that sick before,' Duval said. 'I'm exhausted from it.'
Duval started the final round in a tie for 10th, seven strokes out of the lead. He carried a portable seat and rested between shots, but his swing looked lethargic and he let one hand go on his follow through.
'I just didn't have the energy to walk or swing,' Duval said, who had a birdie and two bogeys before walking back in.
He weighed himself out of curiosity Sunday morning and was at 167 pounds.
Next up is the Match Play Championship at La Costa, where Duval is the No. 3 seed. He planned to drive down the coast Sunday afternoon and said he expected to play. Duval faces Kevin Sutherland in the first round.
Still, this has been another forgettable West Coast Swing for Duval.
He tied for 12th at Kapalua, was never a factor at the Bob Hope and then took off three weeks, during which he split up with his fiancee. Duval returned at Riviera feeling fresh and swinging well, but figures a sandwich Saturday afternoon did him in.
'I guess I won't be king of Swing this year,' he joked, referring to the $500,000 bonus for the player who has the best performance in first eight tournaments of the year.