The 25-year-old, who spent last season on loan at Everton, is a free agent after leaving Madrid at the end of last season.
"We didn't expect this either, but they asked me about his numbers, how much he would cost salary-wise. There are also clubs from the Serie A and Turkish clubs interested and also Dinamo Kiev," Antonio Salerno told Goal.com.
"No complaints about interest indeed, but the most important thing is that Royston gets back on the pitch again. He prefers playing for a club in the Champions League, so City, Kiev and the Turkish big clubs have his favour at this moment."
Drenthe has one Dutch cap to his name.