They said in a statement they were "in discussion with Leeds club officials in relation to this incident".
"I have a different point of view but the important thing is what Frank Lampard and Derby County think".
Derbyshire Police issued a statement denying the reports, but did confirm that "a man was found at the perimeter fence of Moor Farm and was spoken to".
Derby are now eight points behind Leeds ahead of Friday night's match, and lost the corresponding fixture at the start of the season 4-1 at Pride Park.
"It's true there was someone from Leeds United", said Biesla when asked about the incident.
I would say it was our worst performance, albeit against a top team in the league.
The ex-Argentina boss said before the game that he had apologised to Derby boss Frank Lampard, and added that he had used that type of practice "since the qualifiers for the World Cup with Argentina".
The Football Association (FA) will investigate allegations of spying after Derby County claimed a man caught by police acting "suspiciously" near their training ground was a Leeds United employee. Yesterday I talked to Frank and he told me I didn't respect his club.
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"Obviously it's not just Derby County, we had somebody the day before our first game against them which we lost 4-1".
"Of course I don't think it's right and I'm not sure anyone who's played sport at any level would think it's right".
"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".
'What I will say is that we were training the day before the game on team tactics, team shape, personnel, how we are going to press, how we are going to work on the ball, the fact that Harry Wilson wasn't training will become very evident, so the person watching sees all of that.
"If I'm lucky enough to do well and travel to another country I'll find out what the etiquette is in that country and abide by that".
"I don't think we need to [investigate], because he's admitted it so it's easily dealt with".
Frank Lampard's men will take the trip to Elland Road this evening as they aim to inflict a fourth-straight defeat in all competitions on the league leaders.