Thomas Bjorn, winner of the Irish Open two years ago, has pulled out of next week's tournament at Adare Manor near Limerick.
The Dane finished fifth in South Korea in March, but since then has suffered a recurrence of back trouble and in addition to missing halfway cuts in Spain, Portugal and China withdrew from the Spanish Open in Seville last week.
The event has been boosted, though, by Lee Westwood making a late decision to play and he joins a field headed by Open champion Padraig Harrington, Colin Montgomerie and the four Irishmen who have all won on the European Tour in recent weeks - Graeme McDowell, Damien McGrane, Darren Clarke and Peter Lawrie.
Harrington brought to an end a 25-year wait for a home winner last year, beating Welshman Bradley Dredge in a play-off on the same course.
RYDER BOOST FOR McDOWELL
ROYAL BIRKDALE TO TEST TACTICS
WEEKLEY AT CAREER HIGH
LAWRIE LEFT SPEECHLESS
