Rafael Nadal has pulled out of next week’s BNP Paribas Masters in Paris.
“Personal reasons” were cited by tournament organisers in a statement, with US Open champion Marin Cilic also withdrawing because of a right arm injury.
Nadal revealed earlier this month he was suffering from appendicitis, which he has so far managed with antibiotics but will require surgery.
The Paris announcement came while Nadal was preparing for his quarter-final against teenager Borna Coric at the Swiss Indoors in Basle.
It will add to speculation Nadal could pull out of the Barclays ATP World Tour Finals in London next month in order to go under the knife.
The 28-year-old’s team have previously said a decision would be made after this week’s Basle tournament.
Cilic has already qualified for the World Tour Finals courtesy of his grand slam win, although he is not yet guaranteed of a top-eight finish.