Graeme McDowell has pulled out of this week's PGA Tour Wells Fargo event at Quail Hollow.
The 2010 US Open champion said that he felt "under the weather" at last week's Zurich Classic.
"Very much wanted to play Quail Hollow but didn't want to go there undercooked. Practice and rest for me this week," McDowell said on Twitter.
Rory McIlroy will be in action at the Quail Hollow event where he claimed his first PGA Tour win in 2010.
He will defend his US Open title in six weeks' time and is expecting the Olympic Club course in San Francisco to be a tougher test than last year's Congressional venue.
The Northern Irishman knocked four shots off the US Open championship record as he shot 16 under par last year.
"The thing that made the scoring low was the fact they got so much rain before," said McIlroy.
"Last year was a bit of an exception. I'm expecting something around level par isn't going to be too far away."
That was the score with which Lee Janzen won the title the last time Olympic staged the event in 1998 - and Jack Fleck and Ben Hogan tied on seven over par back in 1955.
Pebble Beach was firm when Graeme McDowell won two years ago, with McIlroy missing the cut on that occasion.
"At that point I was not playing so well," the 22-year-old added. "I was not in control of my ball."
The recent Masters was billed as McIlroy versus Tiger Woods in some quarters, but it did not turn out like that.
"It was a two-horse race for 40th," joked McIlroy, remembering that they finished level.
Nobody has made a successful defence of the US Open since Curtis Strange in 1989.