Leeds boss Marcelo Bielsa has admitted he did send someone to spy on Derby's training, but has not apologised for the incident.
Derby say a Leeds employee had to be removed by police from the perimeter of their training ground ahead of Friday night's Championship match between the clubs.
Derby manager Frank Lampard suspended training and took the players off the pitch after the 'spy' was discovered.
Asked about the incident before facing Derby, Bielsa told Sky Sports: "It's true it was someone from Leeds United. I am responsible for it. It doesn't matter if this is legal or illegal, or right or wrong... for me, it is enough that Frank Lampard and Derby felt it was not the right thing to do, for me to believe that I didn't behave well.
"Yesterday I talked to Frank Lampard and he said I didn't respect the rules of fair play. I have a different point of view on it, but the important thing is what Frank Lampard and Derby think.
"I am the only one responsible for it, because I didn't ask for the permission of Leeds to do it.
"Without trying to find a justification, I have been using this kind of practice since the qualifiers for the World Cup with Argentina. It is not illegal, we have been doing it publicly and we talk about it in the press. For some people, it's the wrong thing to do and for other people, it's not the wrong thing to do."