The Scottish SPCA, supported by police, raided two properties on the £17.5 million Millden Estate in the Angus Glens last week, according to a report in The Herald.
The estate is widely regarded as the "holy grail" of grouse moors, according to the newspaper.
Computer equipment was taken from the estate with allegations that dead buzzards were also found.
However, there is no evidence available on how the birds died.
The estate said it was co-operating with the investigation, which centred on one of its employees rather than the business itself, the newspaper reported.
A spokesman for Millden Estate told The Herald said: “The estate understands that the investigation by Police Scotland and the Scottish SPCA relates to alleged animal fighting. The estate is not the focus of that inquiry.
“It understands that the inquiry is at a very early stage and is carrying out its own internal investigation.
“In the interim, an estate employee was immediately suspended in accordance with our procedures.
“The estate will continue to liaise with the appropriate authorities.
“It has a robust system of compliance with the law including a zero-tolerance approach to any wildlife offences or animal welfare issues.”
The Scottish SPCA earlier this week issued a formal statement saying it had carried out raids in both Angus and Aberdeenshire as it investigated animal fighting.
It did not say exactly where the raids were but did say it had rescued dogs. An undercover officer in the charity’s special investigations unit said: “We uncovered intelligence to suggest illegal animal fighting was taking place at these locations.
“With serious concerns about the welfare of both the dogs and wild animals being subjected to this, we worked with the police and external partners to raid both addresses.
“We’ve seized several animals and will be checking on their condition.”
Police Scotland and RSBP confirmed it had supported the operation.
Ian Thomson, RSPB Scotland’s head of investigations, said: “We provided background information to the Scottish SPCA to assist in their planning of this operation, and we have been kept up-to-date with recent developments.”