Guus Hiddink says Radamel Falcao's latest injury is "very serious" and has set no time-frame on the Chelsea forward’s return.
Falcao joined Chelsea on a season-long loan from Monaco in the summer, but has not featured since the 3-1 defeat to Liverpool on October 31 after picking up a thigh injury.
In that time, Jose Mourinho has been replaced by Hiddink and the Dutchman has admitted he expects to be without Falcao for a significant period.
"There are still many months to go, so that's too far," he said. "We're almost at the end of January, then February, normally six, seven, eight weeks with serious damage. It's very serious.
"It's a pity for him because he's very eager to come back. That's a bit of the problem -- he was so eager the previous time and wanted to prove himself maybe a little bit too much to me, and then he fell into this injury again.
"If you've been one of the star players in Europe scoring many, many goals and then you have these [injury problems] at the age in which you want to perform in your career, it must be very hard for him."
Falcao endured a difficult time on-loan at Manchester United last season, scoring just four goals in 29 appearances.
The 29-year-old has been blighted by knee injuries during his career and, as a result, there have been question marks over his fitness and whether he can still compete at the highest level.
His latest injury scuppered a return to parent club Monaco, where he failed a medical according to the French club's owner Vadim Vasilyev.
Hiddink insists he will not attempt to rush Falcao back too quickly and will wait until he has fully recovered.
"The medical staff and physical staff will bring him to me when he is recovered, and we haven't set a time on that," he added.
"We'll give him time to recover because he's always dropping back into physical problems. Normally I like to put a little pressure on [the medical staff] to have the player available, but in this case I'll step back and let them deliver a fit player to me."