After his World Cup exertions with South Korea, Park has struggled to find any kind of form since returning to Old Trafford.
His first-half display in Valencia last night was particularly poor as the 29-year-old repeatedly gave away possession when Alex Ferguson had demanded his team retain it.
At one point, the United boss delivered a stinging volley at Park to try to trigger some improvement.
The move worked and Park completed the full 90 minutes of the excellent 1-0 win at the Mestalla stadium.
But he is still not happy with his own contribution.
He said: "I am not satisfied with my performances this season.
"I don't know why my performances have not been good. Maybe I was not ready for the season.
"But mentally I have been weak and I have to improve.
"In the first-half last night my performance was bad but at least the second was better."
Ji-Sung admits he's not on song
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so he love to sing KTV but he cannot sing ?????
he ok lar
but not as lazy as torres can lia0
Park Ji-Sung is putting all transfer speculation to one side and is simply concentrating on his football.
Speculation has linked the Manchester United midfielder with a move to Tottenham in January as a makeweight in a possible deal for Gareth Bale.
But the 29-year-old, who scored in the 3-2 Carling Cup win over Wolves on Tuesday, is not thinking about his future at present.
Instead, the South Korea international is looking to get back to his best on the pitch after a sluggish start to the campaign following this summer's World Cup.
He told South Korean media: "I'm not thinking about leaving at the moment. I'll think about my future at the end of the season.
"The win (over Wolves) was a satisfactory result and I am happy with my performance.
"My recent form hasn't been that good so it's good to see progress."
While Javier Hernandez netted a late winner to see off Wolves, Park, who also scored against Scunthorpe in the last round of the competition, always thought United could win against Mick McCarthy's side.
"When we conceded the second goal I thought we still had time and knew we'd have great chances to score again," Park told MUTV.
"We always believe we can score. Everybody expected him (Hernandez) to score when he came on and we all know he has the ability. It's important for him to keep scoring goals and we believe he can."
He added: "We played well in the first half but couldn't finish anything. At half-time we said we needed to concentrate more in the last third of the pitch.
"In the second half we did that and we made some great chances and scored some great goals. Today I scored, which makes it two goals in a row for me in the Carling Cup. It's great to score in any competition."
Park hailed Sir Alex Ferguson's policy of blooding young players in the competition after United gave Ben Amos his second senior appearance in the game, while Bebe enjoyed his first senior start and 17-year-old Ravel Morrison came on as a substitute after Hernandez had sealed the win.
He added: "Manchester United has always had talented youth players and has always given opportunities to young players.
"It makes the squad stronger and from this opportunity they'll improve and gain more confidence. It's good for their future."