Zadkovich, 21, is in the second day of a four-day training stint at the Rams, who’ve been relegated from the EPL and are preparing for life in the Championship next season.

The Rams already have newly-signed Aussie Mile Sterjovski in the squad who's only just fighting his way back to fitness after signing for the doomed club in January.

Sources at County say the young Aussie has made a good impression on coach Paul Jewell with his ability to run all day and chase.

Zadkovich, who has a European passport through his Croatian heritage, knows what it’s like to play in England having had stints with Notts County and QPR between 2004 and 2006.

The Olyroo recently trialled with Championship side Crystal Palace but it’s understood he rejected an offer from the club.

There has also been confusion about what he was doing in England with some reports claiming he was there on a private holiday.

Jets boss Gary van Egmond this week revealed he believed Zadkovich would be signing for Newcastle after his UK trip and had agreed contract details by text message.

But Derby could be willing to make the Olyroo a counter offer as soon as next week.

A club insider revealed: "Ruben is spending the week training with us. At this moment in time it doesn’t go beyond that – but it may do..."