The 25-year-old made just three appearances for The Red Devils in the 2021/22 season as he played second-fiddle to David de Gea.
He has now given a remarkable interview where he has slammed the club for their treatment of him.
Henderson claimed the club promised that he will be the number one after returning from Euro 2020, but that never materialised.
Speaking to talkSPORT, he said: “To be honest with you, it’s probably been the toughest 12 months of his career. It’s been tough. It’s been hard. I’m so happy I’m out here. I’m going to bed now so excited and I’m ready to go.
“The conversation I had, coming out of the Euro  squad, was that you’re coming back here [Man United] to be the number one goalkeeper. I got covid – came back – so I should still have been number one, but unfortunately no one followed through with anything they told me.
“I turned so many good loans down last summer for that reason [being promised the No.1 spot], 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.
“But I worked hard on the training pitch to keep improving day-in, day-out, so I’m really excited to be back here and looking forward to the season with Forest.”
“Nobody followed through with anything they told me. I turned many loans down.”— talkSPORT (@talkSPORT) August 2, 2022
“Wasting 12 months is criminal at my age.”
Dean Henderson hits out at #MUFC in an exclusive interview with talkSPORT. 🚨
Everyone is talking about this 🔥 pic.twitter.com/3CTYoiNwKP
Henderson then admitted he didn’t even speak to Erick ten Hag about his future after the Dutchman was installed as manager.
He continued: “No. I didn’t really want the manager to come in and be able to see me in training because I knew he’d probably want to keep me.”
“I tried to do it [loan to Nottingham] all before [Ten Hag joined]. I told the hierarchy I need to play football. I don’t want to be here playing second fiddle. I was almost gone before the manager came in and I haven’t spoke to him since.”
What an incredible interview. It’s important to note that Henderson is still a United player, so he could yet return to the club next summer and win the number one spot.
After that interview, though, we can’t see him playing for the Premier League giants again.