Pregnant Tian Tian was expected to deliver the cub on August 31, but passed her due date.
Analysis of her hormones last week revealed she is no longer pregnant and may have reabsorbed the foetus – a common occurrence in giant pandas both in zoos and the wild.
Iain Valentine, Director of Giant Pandas for the Royal Zoological Society of Scotland, said Tian Tian appeared to have lost the cub around August 19, when the temperature fell.
He said: “We saw a blip in her hormones in the third week in August. Everyone will remember we had two very warm weeks and then that week it suddenly became very cold.
“We don’t know if that is what did it, but maybe there is something we have to look in to.
“We saw a little blip in the data midweek, from Tuesday August 19 onwards. Everything settled back to normal again after that but that was the first warning that the pregnancy wasn’t going to end nicely.”
He added: “All the way through to August everything was fine. We know Tian Tian conceived seven to ten days after artificial insemination back on April 13.
“That embryo was carried all the way through and started to develop from August but in that third week something went awry.
“It’s quite devastating.”