Hodgson overlooked the 33-year-old Manchester United centre-back for his initial 23-man group for this summer's tournament, dismissing his absence as being for "footballing reasons", and then did so again on Sunday when he called up inexperienced Liverpool defender Martin Kelly in place of the injured Gary Cahill.
Many felt there were concerns about Ferdinand's ability to play with John Terry in light of Terry's impending court case for alleged racist remarks to Ferdinand's brother Anton. Terry denies the charge. Redknapp, who was widely tipped to succeed Fabio Capello before Hodgson took the role, told Sky Sports News: "I think it's a difficult decision for him."
He continued: "There's obviously more to it. If it's just football, it's difficult to leave Rio out, obviously, because he's a fantastic player still.
"But that's the decision that's been made and we've just got to get behind Roy and the England team now, with the Euros coming up. We're all looking forward to it. It'll be a great tournament, I'm sure, and there's no reason why we can't have a great tournament.
"We've lost some key players. Gary Cahill is much improved. He's going to be an excellent centre-half, with a great future. But Joleon Lescott is also a great player in my opinion, and Phil Jagielka. With John Terry as well, there's plenty of cover there and I'm sure we've got enough central defenders to do the job."
He added: "I'm sure the players will come together. I think the spirit looks good. [England have produced] a couple of decent performances - in Norway and at home at the weekend against Belgium, who are difficult opponents.
"Without being spectacular, we were solid, strong, difficult to beat. I'm sure that's how Roy will set the team up and nobody will get an easy game against England."
And Redknapp was not ruling England out of causing an upset, using Chelsea's surprise Champions League victory as proof anything is possible.
"Spain and Germany, from what I've seen, would probably be the favourites, but you just never know," he said. "It's cup football - as you've seen this year in the Champions League, anything can happen."