The 33-year-old South Korean spent seven years at Old Trafford between 2005 and 2012 and played in the 2009 Champions League final - becoming the first Asian to do so.
He won four Premier League titles with United and got a medal as they lifted the Champions League in 2008
He made 205 appearances for them in total.
He joined QPR for the 2012/13 season before returning to PSV Eindhoven - the club United signed him from.
"I didn't cry about it yesterday, and I'm not crying about it today, that means I'm leaving with no regrets," Park told reporters in South Korea.
"I enjoyed playing football
I have achieved more than I thought I would
I'm truly grateful for all the support I have received and I will live the rest of my life thinking how I can pay it back."
Source : PA
Source: PA