Interim manager Benitez was hopeful Terry would be fit to return for one of the Blues' four matches over Christmas and the new year.
But he stressed that he could not "guarantee" that, adding of his captain's recovery: "It's one step forward, one step back."
Benitez confirmed Terry, who had been scheduled to return almost two weeks ago, would definitely miss Sunday's Barclays Premier League game against Aston Villa.
Terry trained without the ball but was still not ready to return to full-contact exercises, with Benitez revealing the defender was prone to an adverse reaction 24 hours after training.
"The knee is quite complicated," he said.
"At least he's now on the pitch - that is positive news - but we cannot say, we cannot predict how long it will take."
Asked if Terry would make his comeback in the next fortnight, Benitez said: "I hope so but I am not a doctor.
"So I cannot guarantee anything."
- Sports & Recreation