London - England's Lee Westwood faces a race against time to regain fitness for next week's Open at St Andrews after being diagnosed on Monday with a slight tear in his right calf muscle.
The world number three aggravated the problem during last week's French Open and so withdrew from the JP McManus Pro-am currently underway in Ireland.
"He's been advised complete rest for the rest of the week, but is still very hopeful that everything will be fine," said management spokesman Martin Hardy.
"He's been convinced that if everything pans out as expected he will be okay."
The 37-year-old went to hospital last Wednesday for a check-up after an initial scare that he might be suffering from a blood clot or deep vein thrombosis, but further tests ruled that out.
Westwood had planned an early visit to St Andrews later this week, ahead of next Thursday's opening day, but that has now been cancelled.
Last July, he bogeyed the final hole to lose by a shot at Turnberry and this April he was runner-up in The Masters.
Meanwhile, Americans Rickie Fowler and Jeff Overton have secured places in next week's Open courtesy of their positions as the highest-ranked players, not already exempt, in the world rankings.
Fowler, ranked 37th, will make his Open debut, while Overton (63rd) will be making a third consecutive appearance and finished joint 13th last year.
One Open place has been reserved for the leading player, not already exempt, finishing in the top five at each of the Scottish Open and the John Deere Classic this week.