The conservator, who spoke on condition of anonymity, told Egypt's state-owned Ahram Online that the mask's beard broke off by accident when the mask fell as it was being cleaned last year at the Egyptian Museum in Cairo.
He said the blue-and-gold braided beard was fixed back in place quickly with epoxy, a type of strong adhesive.
"The epoxy was not a proper material to use to restore the mask, although it is a conservation material with a very high strength for attaching metal and stone," he is quoted as saying.
The conservator said there was now a gap between the face and the beard where the glue had dried.
However, the Egyptian Museum's general director, Mahmoud El-Halwagi, dismissed the claims in an interview with Ahram Online, saying the beard was in its original position and that nothing had happened to the mask since he took up his position in October.
"An archaeological committee was assigned to inspect the mask and beard in order to write a detailed report on the mask's condition," he said.
Minister of Antiquities Mamdouh Eldamaty also told Ahram Online that media reports of damage to the mask were unfounded.
The boy king's elaborate burial mask, discovered in his tomb in 1922, is one of Egypt's most outstanding artifacts.
Tutankhamun, who ruled from 1336-1327 BC, is thought to have been about 17 years old when he died, based on analysis of his mummy, according to the British Museum
. His cause of death is not known.
If confirmed, it won't be the first time a historical treasure was damaged in an institution supposed to keep it safe.
In 2006, a visitor to the Fitzwilliam Museum in Cambridge, England, famously tripped on a staircase
and smashed three hugely valuable Chinese Qing dynasty vases. The thousands of porcelain fragments were eventually painstakingly reassembled