Park did well in the World Cup for his country, but since returning to Old Trafford he has made just one start for the club.
The 29-year-old Park concedes he has not been at his best in the new campaign, but does not believe his disappointing start is a World Cup hangover and is determined to turn things around and show the sort of form we have come to expect from the Korean.
"I know some people haven't been satisfied with my recent performances," he told the club's official website.
"It is not a hangover from the World Cup, but perhaps I was not mentally fully prepared for the new season.
"I'm not worried. You have many ups and downs as a player and I'm sure I will get better. The friendly with Japan will be the first step.
"This international break will be the turning point for me and my performances will improve when I return to United."