The goalkeeper claims that he was promised that he would be first-choice between the sticks at Old Trafford but instead did not play a single Premier League game and lost his place in the England squad.
Henderson has now joined newly-promoted Nottingham Forest on loan and feels that last season was a complete waste of his time.
The player told talkSPORT: "The conversation I had, coming out of the Euro squad, was that you're coming back here to be the number one goalkeeper. I got Covid - unfortunately, no one followed through with anything they told me.
"I turned so many good loans down last summer, and they wouldn't let me go. It was frustrating. To sit there and waste 12 months is criminal really, at my age. I was fuming."
Henderson revealed that he feels like a "caged animal" following a year on the sidelines and is looking forward to the season ahead with Forest as they begin the new campaign against Newcastle at the weekend.
He told Sky Sports News: "I can't wait to get back out there. For me personally, being a caged animal for the last year, to get out there and actually play in front of a full St James' Park, being the underdogs, is sensational."
Henderson revealed that he is desperate to play against United but the loan deal will prevent him from doing so.
He said: "I love playing, the manager has been fantastic with me. I want to play for him. He's shown some good trust in me and I want to show the same in him. Facing Manchester United would excite me the most, but I can't play against them - that's me being honest, I'd love to go toe-to-toe with them."