A keeper in the panda enclosure told a visitor that Tian Tian was giving off hormones that indicate she is about to have her cub.
Only a week ago, hopes began to fade as zoo chiefs openly admitted it was only "possible" Tian Tian was pregnant.
But a zookeeper looking after the bear yesterday gave visitors the impression they are in little, if any, doubt about a happy outcome.
The male member of staff said: "We think Tian Tian will give birth any day now because of a hormone she is giving off."
The keeper also revealed that the male panda, Yang Guang, had been severely affected by the hormone.
"The hormone is making Yang Guang really restless," said the keeper. "Yang Guang has been taken off display because he is sick."
Edinburgh's female panda was artificially inseminated with the sperm of two pandas in April and in July the zoo indicated that they believed she could be pregnant.
The test earlier this year, detected a rise in Tian Tian's progesterone levels.
However, as the zoo have been unable to carry out an ultrasound on the panda, they have never confirmed the pregnancy.
The zoo's "panda team" last month stated that Tian Tian was showing signs of "nesting behaviour," a strong indicator that she is pregnant.
Also, last month the zoo stated that its team of panda keepers were now on twenty-four hour panda cub watch as Tian Tian's hormone levels had continued to rise.
But last week, a zoo spokeswoman admitted there was confusion over Tian Tian's pregnancy, stating that a panda cub was now only "possible" despite earlier confidence.
A spokeswoman for the zoo said: "In terms of Tian Tian's possible pregnancy, we're not out of the game yet although she's keeping us on our toes.
"Her hormones are following an atypical pattern, with lots of rises and dips, which make timings much harder to predict."