Ferdinand's absence has been a major talking point since Hodgson picked his 23-man side last month and his omission was emphasised further when injured defender Gary Cahill was replaced by Liverpool youngster Martin Kelly on Monday.
Hodgson is yet to speak about the matter and FA chairman David Bernstein rebuffed repeated questions over the issue this afternoon.
And Campbell, who played alongside Ferdinand on several occasions for the national team, believes, like many others, that the 33-year-old's omission had nothing to do with "football reasons" as Hodgson previously stated, and everything to do with worries about how the defender would interact with John Terry.
"The further this saga drags on the more it does not make sense and the more it undermines Roy Hodgson and the Football Association as a whole," Campbell wrote in the Guardian.
"We have now reached a point where big questions have to be asked over Rio Ferdinand's exclusion from England's squad for Euro 2012, such as what are the real reasons, and why? And is there a cover-up?"
Terry has a court case pending over alleged racist remarks to Ferdinand's brother Anton at Loftus Road in October, with the Chelsea defender denying the charge against him.
And Campbell continued: "What we can say for sure is that this entire situation goes back to what did or did not happen between John Terry and Anton Ferdinand last season. That is the only logical conclusion that can be drawn and I for one never bought the argument that Rio had been left out of the original squad for 'footballing reasons'.
"The FA now find themselves between a rock and a hard place and the only way they can truly resolve the situation is to come out and admit they've made a mistake.
"At the very least Rio should have been given the opportunity to say 'no, I don't want to be in the same squad as John Terry'.
"Hodgson should have spoken to him man-to-man, face-to-face, eyeball-to-eyeball and seen where he was at, seen if he felt capable of contributing to the team and being around Terry for the next three weeks."
Campbell fears the issue could harm players' trust in the FA and also that it could deter players from reporting cases of racist abuse.
"A wider issue is if this episode leads to players in the future feeling reluctant to speak out against racism in case it harms their chances of being picked by England," he said. "That would be extremely serious and would have to lead to the government getting involved in some way."
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