Freeman asked to go out on loan after finding his game-time limited at United, and joined Forest in the Championship.
But he struggled for consistent fitness after a routine operation was botched, and what he feels should have been a six-week absence eventually ended up affecting him for “five or six months”.
The issue was eventually uncovered when he went under the knife again, but Forest opted not to take up the option to make the move permanent and he returned to United intent on impressing new boss Slavisa Jokanović.
He did those hopes no harm with a headed goal in what turned out to be United’s final pre-season friendly against Doncaster Rovers. And, speaking ahead of this weekend’s season opener at home to Birmingham City, Freeman told The Star: “It was very frustrating.
“I had surgery and got back and didn't feel right. The scans were saying I was fine but I wasn't and it was only when they opened me up again that they saw that it wasn't.
“Then it was back to the drawing board and another few months out. So it was very frustrating because it almost looks like you're lying, saying you're not fit and nothing's showing up on the scan. I wondered: ‘What's going on?’
“I'm happy I got to the bottom of it because I was losing my marbles. I was thinking: ‘Have I gone soft or what?’ I knew it wasn't right and it was proved.
“It was very frustrating when it was supposed to be a quick six-week injury and ended up being five or six months. It wasn’t ideal.”
Freeman established a reputation as one of the second-tier’s most creative talents during his time at QPR.
“I know my own body and picked up another little injury at the back of the season which set me back another two months, so it's been a frustrating year,” he added.
“But all players go through it. It's about bouncing back from that and going again.”