Howell has had a frustrating year

The Englishman, 32, who has yet to earn a top-20 finish in 2007, misses the Gleneagles event, starting on Thursday.

Defending champion Paul Casey is eyeing a third win in the tournament, with Darren Clarke, Lee Westwood and Colin Montgomerie also in the field.

"My lower back's not been working well again but hopefully I'll be back in Switzerland next week," said Howell.

Interview: Scottish golfer Colin Montgomerie

"I was concerned that the stress fracture I suffered earlier in the year had not healed.

"But the scans came back saying that that isn't the case, so I'm a little bit more positive and the new chiropractor I'm seeing is quite happy for me to keep being the golfer I am."

The two-time Ryder Cup star reached number 12 in the world last year and led the European Order of Merit for a large part of the season, helped by winning the Tour's flagship PGA Championship at Wentworth.

But back and wrist injuries have hampered his progress and he is only 125th on the European money list this term and has plummeted to 73rd in the global rankings.

Montgomerie, meanwhile, says he and his wife-to-be are "just thrilled" after becoming engaged at the weekend.

The 44-year-old has been going out with multi-millionairess Gaynor Knowles for a year, his first marriage having ended in divorce.

Montgomerie has three children, while his 40-year-old fiancee has four from her marriage to furniture tycoon George Knowles, who died of a heart attack four years ago.

"We're looking forward to the future together," added Montgomerie, a multi-millionaire himself after winning the European Order of Merit a record eight times.

"We've not yet made any formal plans, but will be planning with the respective families in the coming weeks."