Earnshaw joined Derby from Norwich at the end of June in a club-record £3.5million deal, but according to Plymouth Argyle manager Ian Holloway the 26-year-old is set to move to Charlton before Friday's transfer deadline.
Asked about late transfer business on Argyle's official website, Holloway said: "There's already one! Earnshaw's gone from Derby - already - to Charlton, which seems ludicrous to me.
"There'll be some mental last-minute panic shopping but I'm not in that game."
Derby were refusing to confirm whether the deal would be sanctioned with a spokesman saying: "We refuse to comment on transfer speculation."