David Howell believes his career plans have been heavily dented by a two-month lay-off with back and wrist problems.
Howell has slipped from 10th in the world to 38th in 12 months
The Englishman returns to action in the European Open in Ireland this week having last appeared at the Players Championship in Florida in May.
"I had a masterplan for this year, but that has all just been thrown up in the air now," said the 32-year-old.
"The most frustrating thing is that I put in as much time and effort into my career as anyone."
Howell was ranked 10th in the world a year ago, but has since dropped down to 38th, and since the Masters in April, the Ryder Cup star has played just 20 competitive holes.
This week's event at the K Club, which hosted last year's Ryder Cup, will be the Swindon golfer's first tournament in Europe this year and he admits he is concerned about how his form has been affected.
It's stressful not knowing how well you are going to play
"Apart from one round I've not played for the best part of three months now and golf's all about momentum," he said.
"It's also stressful not knowing how well you are going to play when you do come back.
"I've come back from previous lay-offs and done well straightaway. I wasn't playing well before I got injured and maybe starting again with a clean slate it will be different."
Not returning to the K Club will be Howell's Ryder Cup team-mates Paul Casey, Lee Westwood, Robert Karlsson and Henrik Stenson.
Westwood withdrew with a knee problem that was bothering him at last week's French Open, while Casey has decided not to risk a bruised back muscle.
Not entered for next week's Barclays Scottish Open at Loch Lomond, Casey's next outing will now be at the Open. The Englishman is not thought to be in any danger of missing Carnoustie.
Karlsson's decision to wait until Loch Lomond before playing again means only four of last year's victorious European team are returning to the scene of their triumph - although the course being used this week is not the one used for the Ryder Cup.
The quartet are Irish duo Padraig Harrington and Paul McGinley, Scot Colin Montgomerie and Howell.
Jose Maria Olazabal has a knee injury, while Darren Clarke is having a week off after two events in America. Sergio Garcia and the recently-married Luke Donald return to action next week as well.
The European Open will see the first appearance of Angel Cabrera since his US Open triumph.