The 32-year-old was under scrutiny for a yellow card he received while playing for Blackburn Rovers against Ipswich Town in December, but he was released without charge last month.
He told the Independent on Sunday: "There were times when I seriously considered walking away from football and retiring. But friends and family were very supportive. I guess I was just in a very bad place.
"When I put everything into perspective, I had worked far too hard and made too many sacrifices to give football up. Why should I walk away when I had done nothing wrong? To my enormous relief, I was called back to Winchester police station last month and they eventually lifted my bail conditions and released me without charge.
"There was no cause for celebration. I was relieved but I still felt a great sense of injustice."
Campbell is currently without a club after leaving Blackburn in July.