Stan Wawrinka and Milos Raonic have each withdrawn from the year-ending Mubadala World Tennis Championship (MWTC) through injury, heightening doubts over their readiness for next month's Australian Open.
Wawrinka missed the US Open due to a knee injury, while Raonic sat out the final grand slam of 2017 due to a wrist problem before being sidelined again with a damaged calf.
On Wednesday, the MWTC's official website revealed both players would not be present in Abu Dhabi next week.
Three-time slam-winner Wawrinka said: "Unfortunately I won't be able to play in Abu Dhabi this year as I'm not ready yet to compete at this level.
"Together with my team, I'm working hard and we will do everything to be ready in time for the Australian Open.
"I'm sad that I won't be able to play in front of the great fans at the Mubadala World Tennis Championship but I need to be patient and give my body the time it needs."
Earlier this month, Wawrinka had said: "The goal is to play the Australian Open, even if I'm not 100 per cent."