Britain's out-of-form Colin Montgomerie and American Ben Crane, the 2003 champion, are among 15 late withdrawals for this week's BellSouth Classic at the TPC at Sugarloaf.
Eight-times European number one Montgomerie pulled out after missing the cut in his last four strokeplay events, a PGA Tour media official said on Tuesday.
No reason was given for Crane's absence.
"Montgomerie's manager said he needs to practise on his own, rather than in a tournament, to try to get his game into shape for (the U.S. Masters at) Augusta," 
the Tour official told Reuters.
"Most of the others who pulled out today were because guys were making last-minute changes to their schedules ahead of the Masters." 
The Masters, the first of the year's four majors, takes place at Augusta National from April 6-9.
Montgomerie, 42, has failed to make the cut in three of his last four appearances at Augusta.
Last April, he missed the Masters for the first time since 1991 after dropping out of the top 50 in the world rankings.
Although he produced vintage form for much of last year, winning the Dunhill Links Championship in October and the Hong Kong Open in December, he has failed to spark this season.
His missed cut in last week's Players Championship at Ponte Vedra Beach in Florida followed early exits from the Dubai Desert Classic, the Johnnie Walker Classic in Australia and the Bay Hill Invitational in Orlando, Florida.
Despite the wave of late withdrawals, the BellSouth Classic has attracted four of the world's top 10.
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