It came on the eve of Derby’s trip to Leeds in Friday’s Championship promotion showdown.
Police came to the training ground, and 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.
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.”
Both clubs have been performing well in the Championship this season, with Leeds top and Derby inside the play-off places in sixth.
The Rams are eight points behind the league leaders heading into Friday’s tie, with Leeds looking for their first win in four games.