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, Press Association Sport understands 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.
County chief executive Peter Trembling told the club's website, nottscountyfc.co.uk: "While we are disappointed that Sol felt that he could not adjust to the long-term nature of the project under way at Notts County, we obviously wish him the best with the remainder of his career and hope that he is able to obtain a place where he can play at international level ahead of the 2010 World Cup.
"The investment project is on track; we have brought in a lot of new players and resources into the club, but obviously this is a five-year project, not a five-week one."
The former England defender was the most high-profile recruit to the playing staff this summer following County's takeover by Munto Finance and Sven-Goran Eriksson's arrival as director of football.
The takeover deal is now being investigated by the Football League and, after making his debut in last Saturday's shock 2-1 defeat at Morecambe, Campbell appears to have had a change of heart.
"For any fan that bought a new Notts shirt and had 'Campbell' printed on the back, I am pleased to offer a voucher for the club shop for a replacement shirt," Trembling added.
He told Sky Sports News: "We're disappointed Sol has decided, from yesterday, he wants to end his contract.
"It's one of those things, he joined five weeks ago on a five-year contract as part of the long-term project, but ultimately he's come to the point, having been here five weeks, where he has decided it's not for him.
"Sometimes decisions are made, people make wrong decisions and Sol has decided this is not where he wants to be now.
"We're not going to kick up a fuss about it. If he wants to go, he needs to go and we genuinely wish him all the best."
Asked about the reasons Campbell gave, Trembling added: "Not an awful lot, just that this was not working out for him.
"I spoke to his representative this morning and he has just decided it's not working out and he wants to move on. Perhaps things are not happening as quickly as he thought they might, but this is a five-year project, not a five-week project. We can't just become a Premier League club overnight.
"That is how it is. If he doesn't want to play here, we don't want him here."