(CNN) -- Park Ji-Sung's Manchester United return has been put on hold after the South Korean midfielder suffered an injury in training.
The English Premier League leaders had been without the 29-year-old for the past six weeks while he was at the Asian Cup in Qatar, and he now faces another month on the sidelines.
Park injured a hamstring injury on Friday ahead of the Manchester derby, and will now miss United's European Champions League last-16 clash with Marseille in France on February 23.
"It was very unfortunate because it was his last kick of the ball in training," team manager Alex Ferguson told the club's website on Tuesday.
"We were really looking forward to having him back after being away for a month at the Asian Cup. He'll be out for up to a month, which is a blow to us."
The winger has not played for the English Premier League leaders since the 2-0 win over Sunderland on December 26.
Park was part of the South Korea squad which reached the semifinals of January's Asian Cup before losing to eventual champions Japan.
The former PSV Eindhoven star announced his international retirement after the tournament, citing a persistent right-knee injury as one of the reasons for his decision.
Park will also miss Saturday's FA Cup fifth-round match with non-league minnows Crawley Town as well as Premier League trips to Wigan, Chelsea and Liverpool, but may be back in time for the second leg against the French champions on March 15.
In better news for United, Ecuador winger Antonio Valencia is back in training after breaking his ankle in a Champions League match against Scottish side Rangers in September.
"Valencia started training with the reserves on Saturday," Ferguson said. "So he's on his way back and that will be a real boost to have him available for the run-in."
Valencia signed from Wigan for a reported $27 million in July 2009. The 25-year-old was a regular as United finished second behind Chelsea, but has made only two league appearances this season.