Robin Soderling has suffered a setback in his recovery from glandular fever.
The Swedish star has not played since July due to the illness, also known as mononucleosis.
He had planned to be back in action this month but has now revealed that won't happen and no new return date has been set.
Soderling, who has slipped from fifth in the world rankings to 14th during his period of inactivity, said: "I was hoping to be ready for tournaments in February but unfortunately I am not there yet.
"The good news is that the symptoms of the 'mono' like sore throat and fever are gone, but for some reason my body still cannot handle intense training.
"I get very tired when I do something physical. I am working with my medical team to understand why and what the next step is. My full focus of each day is to get healthy and strong.
"Hopefully it won't be much longer but I cannot compete until I am 100 per cent fit."
