"It's true there was someone from Leeds United. I am responsible for this incident," ex-Argentina manager Bielsa said before the game at Elland Road which Leeds won 2-0, extending their lead at the top of the table to five points.
"I am the only (one) responsible for it because I didn't ask for the permission of Leeds United to do that."
The club's Italian owner Andrea Radrizzani has met with his Derby counterpart Mel Morris to apologise for Bielsa's actions.
The Yorkshire club issued a statement on its website https://www.leedsunited.com/news/team-news/24390/club-statement on Saturday saying it will "look to work with our head coach and his staff to remind them of the integrity and honesty which are the foundations that Leeds United is built on".
Leeds are three-time winners of the English top flight and have also won the FA Cup and League Cup as well as being runners-up in the European Cup and now defunct Cup Winners' Cup.
The FA is investigating the incident, while a Football League spokesman said: "It is, of course, up to Derby County as to how they progress this matter, but as of yet we have received no complaint or contact from the club."
On Friday Bielsa said: "I understand (Derby manager) Frank Lampard is angry because he thinks I'm someone who is cheating.
"I understand he draws this conclusion. But I don't feel I cheated because my goal was not to get an illegal advantage.
"I can explain my behaviour but my intention is not to be understood or to justify it. I have to respect the norms in the country where I work."
Lampard, a former Chelsea and England midfielder, said the situation was "not right" and had to be dealt with.
"I've never heard of going to a training ground on your hands and knees with pliers trying to break into private land to watch," Lampard told the BBC.
"But I don't attribute our performance (in the defeat at Leeds on Friday) to it, because that's on us." (Writing by Ken Ferris; Editing by Mark Heinrich)
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