According to Eurosport, Jurgen Klopp wants to replace Italian international Ciro Immobile in January with PEC Zwolle loan star Tomas Necid, who is out of contract at the end of the season. The report goes on to state the German side are not the only ones, with Feynoord and Ajax also watching the player.
Both players have started the season well, with Necid on eight and Castaignos on nine goals in the Eredivisie, and both could be on the move this January.
Derby moved quick to sign up Aston Villa frontman Darren Bent this January, who joined on loan until the end of the season, but the Sun newspaper reported more strikers could still be recruited before the window closes.
The Rams have enjoyed a busy start to the year, with three players already signed, and one more reportedly in the pipeline. So, the reports that the East Midlands side will strengthen have been proved correct.
Nevertheless, if both Ajax and Dortmund are in fact interested in the 25-year-old, it could prove to be too much for the Rams to battle against.