Although he signed on a free transfer, the deal was a costly one, with Campbell pocketing a signing fee and about £40,000 a week for his bit-part role .
A club source told the Daily Express: "Sol has not really been involved and is clearly winding down his career, seeing out his time and being clearly unhappy with his injuries.
"The club offered a settlement on his contract so that he could walk away after the season ends but he refused. Instead, there is a clause that allows him to take another month's money and he is going to eke out his final pay cheque in July for another £160,000.
"It leaves a sour taste. He clearly doesn't need the money and, if he had any honour, he would go in June."
Campbell's arrival followed a determined push for the player by former manager Chris Hughton.
Our source added: "Campbell's arrival and performances were certainly seen as a factor in the decision to part company with Hughton."