Irishman Peter Lawrie is among seven withdrawals from Monday's US Open qualifying tournament at Walton Heath, Surrey.
American Notah Begay, England's James Hepworth, Simon Wakefield and Robert Rock, former Open champion Paul Lawrie, Spaniard Alvaro Quiros and Indian Jyoti Randhawa have also pulled out of the 36-hole event.
It leaves only 65 players, including Darren Clarke and Paul McGinley, competing for around nine places at Oakmont.
Two years ago, New Zealander Michael Campbell came through the qualifier without a shot to spare and went on to win his first major title at Pinehurst.
After missing his last five halfway cuts and struggling with a hamstring strain, Clarke is having to enter a qualifier for a major for the first time since the 1995 Open.
He is down to 93rd in the world, while McGinley, a fellow hero of the last three Ryder Cup victories, has fallen all the way to 133rd.
Spain's Pablo Martin, who on April 1st became the first amateur to win a European Tour event, will make his professional debut this Monday - as he looks for qualification in Columbus, Ohio.
The 20-year-old, who beat Raphael Jacquelin by one at the Portuguese Open, will be among 144 players competing for 24 places in the starting line-up at Oakmont.
Martin, who resisted the temptation to cash in on his win immediately and went back to Oklahoma State University, faces stiff competition.
Also in the field are former Open champions Tom Lehman, Mark O'Meara and Mark Calcavecchia, ex-US Open winner Steve Jones, 1993 US PGA champion Paul Azinger and a host of US Tour winners.
Victory in Portugal - in just his fifth European Tour start - would have been worth €279,000 to Martin if he had been able to collect it, but because of his amateur status it went to runner-up Jacquelin instead.
The last amateur to win a professional event in Europe before him was Ireland's Dr David Sheahan at the 1962 Jeyes Tournament at Royal Dublin. But that came before the formation of the Tour.
Phil Mickelson was the last player to do it on the US Tour - at the 1991 Tucson Open.
