But Watson, a New Testament scholar at Durham University in England, argued in several brief papers over the last week that the fragment is entirely derived from the Gospel of Thomas. Of particular concern, he writes, is the beginning of the first line, which is identical to the start of a line in the only surviving copy of Thomas. Modern editions of Thomas, which are widely available, include the Coptic with the original line breaks.

But King said it is common for stories to overlap in New Testament gospels. She points out, for example, that the Gospel of Matthew has Jesus saying, in his Sermon on the Mount, “Blessed are the poor in spirit,” while Luke has him saying, “Blessed are the poor . . . woe to the rich.”

Stephen Davis, a professor of religious studies at Yale University, said his cursory reading of Watson’s argument did not seem to rule out authenticity.

“A pastiche of earlier texts — sure it could be a modern phenomenon, but it could also be an ancient phenomenon,” he said. “There are other examples in antiquity of people drawing different texts together.”

Mark Goodacre, a New Testament scholar at Duke University who posted Watson’s ­papers on his blog, said that while King is a cautious, careful scholar who is “massively respected in the scholarly guild,” he found Watson’s arguments persuasive.

“The observations he made were pretty damning for the possibility that this is authentic,” he said. “It speaks to someone who is copying out of our one extant witness of the Gospel of Thomas, not someone translating a Greek original.”