Derby County have said the person police spoke to acting suspiciously outside their training ground on Thursday was an employee of Leeds United's football staff.
The sixth-placed Rams visit the Championship leaders on Friday.
They said in a statement they were "in discussion with Leeds club officials in relation to this incident".
The BBC has asked Leeds for a response, having said earlier on Friday they would not comment on initial reports.
Derbyshire Police said officers were called to Derby's training ground on Thursday morning and a man was spoken to at the perimeter fence.
They added: "No damage to the fence was found, and... no arrests were made."
The English Football League have told the BBC that it is a matter for the two clubs to resolve.
More to follow.