The Korean midfielder spent nine months on the sidelines last term, after damaging knee ligaments in March 2007 and only returned to first-team action in January 2008.
The 27-year-old has been left out of his nation's Olympic side as he attempts to improve his fitness, and is facing a knee-scan on his England return.
He said: "I had a good rest. Many chances will come along during the coming year. What's important is how I grab those chances. It's most important that I show all I can on the pitch.
"It's crucial that I spend the coming season without any injury.
Training will be scheduled according to the test result."