Sky Sports news says United are keeping tabs on South Korean youngster Ki Sung-yong.
According to reports in Korea, the Premier League champions are keen to take the Under 23 star on a two-week trial.
However, FC Seoul have dismissed rumours that United have invited the player over to England to train with Sir Alex Ferguson's side.
"We haven't heard from United or received any formal documents," a club official told local press.
"It is the middle of the (K-League) season now, so organising a trial would be very difficult."