Argentine coach Marcelo Bielsa is known for his meticulous planning and attention to detail when it comes to preparing his teams for matches.

He took it too far this week.

Bielsa, as coach of English second-tier team Leeds, has accepted responsibility for having a club employee spy on opponent Derby County's training session ahead of their league match on Friday.

"Without trying to find a justification, I have been using this kind of practice since the qualifications for the World Cup with Argentina," said Bielsa, who coached his country from 1998-2004. "This is not illegal. We have been doing it publicly; we talk about it in the press. For some people it is the wrong thing, for others it's not."

Police were called to Derby's training center on Thursday following reports of a man "acting suspiciously outside the premises." The man was seen at the perimeter fence, inside which Derby's players were training. British newspaper The Daily Mail reported he had in his possession a pair of binoculars and a change of clothes.

Derby manager Frank Lampard brought an early end to the training session.

"Yesterday I talked to Frank Lampard and he told me I didn't respect fair play," Bielsa said. "I have a different point of view on it but the important thing is what Frank and Derby think. I am responsible for it because I didn't ask for Leeds United permission to do it.

"It doesn't matter if this is legal, illegal, right or wrong," Bielsa added. "For me, it's enough that Frank Lampard and Derby County felt it was not the right thing to do. I didn't behave well."

Lampard, the former England and Chelsea midfielder, suggested the same thing happened before the teams' first meeting of the season.

"We had somebody the day before our first game against them, which we lost 4-1," Lampard said. "Now Leeds can beat you 4-1, they're a fantastic team, but we had somebody in the bushes that day. Twice this season now."

Bielsa's Leeds was top of the League Championship going into Friday's match against sixth-place Derby.