Derby have made a complaint to the Football League over the "spying row" with Leeds United.

Mirror Sport revealed on Thursday that police were called to the Derby training ground and Frank Lampard even had to stop the session while a suspect was detained.

And it is believed that police have traced the suspect's car back to being owned by Leeds United, although police will not confirm details as no arrests were made.

But the row has blown up ahead of Friday night's Championship promotion showdown at Elland Road.

Derby are going public to try and out Leeds United who have made no comment about the row.

(Image: Daily Mirror)

A Derby statement on Friday morning said: "Derby County Football Club can confirm that officers from the Derbyshire Constabulary were called to the Derby County Training Centre at around 11:20am on Thursday 10th January 2019 following reports of a man acting suspiciously outside the premises.

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"It has since been confirmed to Derby County that the individual concerned is an employee of the footballing staff at Leeds United Football Club.

"The club is now in discussion with Leeds United club officials in relation to this incident.

"At this time no further comment will be made."

(Image: Getty Images)

The Football League will now be under pressure to act on the Derby complaint.

Police went to the training ground on Thursday morning, even went onto the pitch before a man with pliers and binoculars was questioned by a fence.

The man was later released after being questioned but Derby police put out a tweet from the Response Unit.

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It read: “Officers have just attended the Training Ground for @dcfcofficial After a suspicious male was seen at the perimeter fence.

“Excellent searching conducted & male was located. All checks above board! Keeping the team safe to bring home a win against #LUFC on 11th! #SpyingIsCheating.”