The defender ruptured his anterior cruciate ligament against Manchester United in September 2012 but returned to first-team action as a substitute in a Capital One Cup tie against the same opponents almost a year later.
Kelly has since made two further appearances off the bench and the 23-year-old is confident that he is nearing full fitness, having also featured for the club's Under-21s on Monday.
"It was a good chance for me to get some minutes," the Anfield academy graduate told The Liverpool Echo. "I'm feeling a lot sharper. I've been doing some additional training over the past few weeks and I'm ready to push on.
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"It's been difficult to get game time as the manager has to pick his best XI to start every game. I was just made up to get on against West Ham and now I need to keep progressing. I've been working hard and I feel a lot fitter than back in pre-season."
The Englishman confesses that it had been a long road back from what can be a career-ending injury but feels that the worst of it is now behind him.
"I don't think there's been a mental barrier to get through, as such, it's more about not feeling as sharp as I wanted," he added.
"Ask anyone who has had a long-term injury and they'll tell you it's tough to get back to that level you were at before the injury. It takes time and it comes back slowly. Now I'm back nearly to peak fitness and I'm ready to go."