The South Korea international was one of the Premier League's most exciting newcomers when he signed for the Trotters in July 2009 and capped his debut season with the club's Player of the Year and Players' Player of the Year awards.
His promising career was put on hold after suffering a broken leg against Newport County in a pre-season friendly and only played in the final two matches of last term.
Since then, the 24 year-old has slowly regained his form and even attracted interest from Premier League clubs in January, although no deal materialised.
He is now confident that he can become even better before the end of the current campaign.
"It feels good to be back and I am really enjoying playing regular football," Lee told The Bolton News.
"When I originally made my first-team return, it took me some time to get up to the speed of the game.
"Now that there is no more pain in my leg from the injury, I feel that I can be getting better and better with every game I play.
"The more games I play, the more confident I feel, and I believe that I can continue to develop and reach higher levels than before my injury."