An archaeological survey has confirmed Hadrian's Wall is damaged where the famous Sycamore Gap tree was cut down.
Historic England (HE) said there were cracks and fragments broken off two facing stones which it believed were caused by the vandalism.
The tree, which stood in a dip in the Northumberland landscape, was felled by a chainsaw in September, on to the World Heritage Site's Roman wall.
Northumbria Police has arrested four people in connection with the felling.
A spokesperson for HE said last month that some damage had been identified but added that experts would be assessing the extent of it.
Posting on social media on Tuesday, it said: "We've carried out an archaeological appraisal of the damage to Hadrian's Wall and can confirm there are some cracks and fragments broken off from two of the facing stones, which we believe have been caused by the felling of the sycamore tree."
The spokesperson said HE had passed the information to police and that it was working with the National Trust on a plan to repair the damage.
It was also carrying out analysis to age the felled tree, which has been taken away for safe-keeping while a decision is made on what to do with it, they added.
The 50ft (15m) tree was among the UK's most photographed and was made famous in a scene in Kevin Costner's 1991 film Robin Hood: Prince Of Thieves.
It was looked after by the Northumberland National Park Authority and the National Trust.