The 29-year-old had only resumed training last week after returning from the Asian Cup in Qatar.
“We got a blow on Saturday with the news Ji-sung Park did his hamstring on Friday afternoon in training,” United boss Sir Alex Ferguson told ManUtd.com.
“He’ll be out for up to a month, which is a blow to us.”
“It was very unfortunate because it was his last kick of the ball in training as well,” Ferguson added.
“We were really looking forward to having him back after being away for a month at the Asian Cup.”