Tomas Berdych's appendix problem has returned to force the world number 10 to stand down from his position as first alternate for the ATP World Tour finals.
The Czech, who withdrew from the US Open with the problem in August, conceded that he does not know how the issue will be addressed.
With the Australian Open around 10 weeks away, the 31-year-old will hope for a swift resolution.
"After discussion with doctors in Prague Hospital I was recommended to have a break for two weeks and then we will see what they gonna do with my appendix," he tweeted.
Berdych reached the quarter-finals of the Paris Masters on his last outing, when he was beaten by eventual champion Andy Murray.
He won just one title in 2016, claiming the Shenzhen Open in October - a result which boosted his hopes of qualifying for the end-of-season Finals in London.
David Goffin has taken the 2010 Wimbledon finalist's place as first reserve.