Professor Patrick Bateson, who is adviser to the Trust, attended a meeting at King's College at the weekend where scientists agreed there was no evidence that stress-induced blood changes in hunted deer were "clinically significant".
The findings have prompted rural pressure group Countryside Alliance to call on the Trust to look again at its decision.
Policy officer Nigel Burke said: "Professor Bateson's two [original] claims about the welfare of hunted deer, on their blood chemistry and their muscle chemistry, have been contradicted by new science.
"The claims of the earlier study that the National Trust relied upon to ban stag hunting were not supported by the scientists present at the meeting. It is reasonable to expect the National Trust ... to reconsider the scientific basis of its decision."
Professor Bateman said he would report to the Trust but restated that "hunting without doubt causes suffering to deer".
The Trust banned stag hunting on its land in 1997 and says it will consider any further research so long as it is as rigorous as Professor Bateson's.
Trust spokeswoman Caroline Audemars said: "The data from both studies suggests that deer may experience suffering as a result of being hunted, and that at least some deer experience a high level of suffering.
"The National Trust Council has said that where the interpretation of data varies it would give the deer the benefit of the doubt."