The 25-year-old, who suffered the injury in a League Cup victory over Chelsea, was forced to undergo surgery on his anterior cruciate ligament and missed the rest of the 2011-12 season.
Having remained injury free for much of his time at Anfield, Lucas says he worried about his career when the length of his spell on the sidelines was confirmed.
"It has been very hard for me because I have never been out for a month so you can imagine five months when I can't play and only watch the game," he told the club's official website.
"I just had to cope with the injury and the time. As soon as I got the injury I knew I would be out for many months and I started to think about other things.
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"To be honest, for a few moments I thought I couldn't come back or even walk, because the way I looked at my knee I felt scared. But as soon as I started the rehab, it is unbelievable how your body reacts."
Lucas is now stepping up his comeback from the injury and is hopeful of returning in time for the start of the new campaign.
He will be playing under a new manager at Anfield after Kenny Dalglish was dismissed and replaced with Brendan Rodgers by the club's owners.
"I think I am progressing very well in terms of the knee, strength and fitness-wise," Lucas added.
"I am working every week and trying to improve every week and the main target is to be fit for the new season."