Former European number one Robert Karlsson has pulled out of this week's British Open.

"Have got into some bad habits in my game and routine that I need to address. Taking a few weeks off," said the 42-year-old Swede on his Twitter account on Wednesday.

Karlsson, who won the European order of merit in 2008, will not be replaced in the Open draw and the field is reduced to 156 players.

His withdrawal has meant a late adjustment to the tee times in Thursday's opening round.

The first group will now go out at 6.30am, instead of 0619, with South African Garth Mulroy joining Briton Barry Lane and American James Driscoll in a three-ball.

Britain's Richard Finch, who was due to go out in a two-ball at 6.30am, now takes Karlsson's spot at 1.10pm alongside American Mark Wilson and South African Branden Grace.

The Swede made his Open debut at Troon in 1989 and has a poor record in the third major of the season. Karlsson has missed the cut 10 times in the event and has recorded only two top-10 finishes.

The North Carolina-based player has struggled on the US and European tours this year, with his best result a tie for 12th place at the Volvo Golf Champions in South Africa in January.