Former England defender Campbell has quit County after just one game, with the League Two club confirming he had left "by mutual consent" after asking to cancel his contract.
However, it is believed that under FIFA rules, Campbell is highly unlikely to be allowed to join another club having severed his ties with County. As an unattached player, a loan deal would obviously be out of the question.
According to the Premier League, only if the veteran can prove he has a just cause for quitting Meadow Lane - a change of heart or minor disagreement, for example, would not qualify - would he be able to sign for a top-flight team while the window is closed.
Campbell, 35, left Portsmouth in the summer and signed a lucrative five-year deal reportedly worth £40,000 a week at Meadow Lane just a month ago, making his first and only appearance in the defeat by Morecambe last weekend.
Reports this morning claimed the centre-half had quickly become disillusioned with the club's rate of progression in that short period.