Woods had until 5 p.m. Friday to enter the Memorial, and tournament officials held out hope until the final minute.
'We're respecting his decision to come back when he's ready,' tournament director Dan Sullivan said. 'There's always disappointment when a top player doesn't come to a tournament. Hopefully, he'll come back next year.'
Nicklaus did not enter for the first time since the tournament began 30 years ago. He said last year he was ending his competitive career in the British Open at St. Andrews, where he missed the cut.
'Kind of a double barrel,' Sullivan said.
The Memorial still has a strong field, with seven of the top 10 players from the world ranking, minus only Woods, David Toms and Luke Donald. The headliner shifts from Woods to Masters champion Phil Mickelson, playing the Memorial for the first time since 2002.
Woods has not played since he tied for third at Augusta National on April 9. His father, Earl, died May 3 in California, and Woods already has missed two tournaments he typically plays -- the Wachovia Championship and Byron Nelson Championship.
It was thought he would play the Memorial to give him one tournament before the U.S. Open on June 15-18. Indications late this week from Woods' camp are that he will play at Winged Foot.
Woods has never missed the Memorial since his first full season on the PGA Tour in 1997, winning three straight years from 1999-2001, and finishing no worse than a tie for fourth over the last three years.
Aside from the four major championships, the only tournaments Woods has never missed are the Bay Hill Invitational, The Players Championship, the NEC Invitational and the Tour Championship.
The Memorial is one of the premier events on the PGA Tour, created in 1976 with Nicklaus as the host and the Masters as somewhat of a blueprint. Nicklaus is often tinkering with the course, caddies where white coveralls, there are no volunteers carrying scoreboards with each group and the staff at the club wears green jackets.
It is sold out again this year, although this will be the first time officials see how much of a difference it makes having Woods.
'It will be an interesting gauge,' Sullivan said. 'But I think there's enough star power on tour -- Mickelson, Jim Furyk, Ernie Els, Retief Goosen, Vijay Singh -- that the tour is as strong as it's ever been.'
The Memorial starts Thursday with Bart Bryant as the defending champion.