Bielsa’s Leeds beat Derby 2-0 at Elland Road on Friday night – then he admitted he send someone to spy on Derby’s training.
Derby claim a Leeds employee had to be removed by police from the perimeter of their training ground ahead although Bielsa has not apologised for the incident.
But Nicholas said: “I take it that it’s not sportsmanlike but any angle you can take in the modern day game.
“Are you telling me Frank Lampard in the past, with team-mates in the opposition, that they don’t find out who’s in and who’s out? What’s the dramatic difference?
“If someone is suspiciously hanging around the training ground, it happened a lot in my day. It’s just something you expect.
“Now the modern way is everything has to be professional – well it’s all about results.
“You might not like it, it might not suit you, and I have to acknowledge Frank Lampard.
“After the match he gave no excuses, the best team won and it’s something else to talk about.”
Derby manager Frank Lampard suspended training and the Football Association are investigating the incident.
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.”