Park, who underwent an operation in the United States in April, arrived on Sunday in his native South Korea and will join up with the United squad on their pre-season tour later this week.
"I will be able to be back playing in January of next year," Park was quoted saying in local sports daily Sports Seoul.
Park said his knee was healing well but that he would have to start months of intense rehabilitation when he returns to England next month.
"It is very disappointing news but hopefully we have the squad to cover injuries this year," United manager Alex Ferguson said.
Park, 26, joined United from Dutch club PSV Eindhoven in 2005.
United play FC Seoul on Friday, three days after a game against Japanese team Urawa Reds. The Premier League champions complete their tour with matches against Chinese teams Shenzhen FC and Guangzhou Pharmaceutical FC.
