The Korean is currently with his national team for the friendly clash with Japan, but has his mind on club matters.
He said: 'I know some people haven't been satisfied with my recent performances.
United we stand: Park Ji-sung (right) in action against Valencia last month
'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.'
On national duty: Park trains with Korea's squad ahead of their friendly clash with Japan
United have had a strange start to their Premier League, with points dropped in every one of their away matches so far.
The Reds will badly want to beat West Bromwich Albion at Old Trafford on Saturday.
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