Reports that the 17-year-old was due to have a training stint with the Premier League leaders were initially dismissed by United.
However, a spokesman for the club confirmed on Thursday that United were trying to sort out arrangements to bring Adu over to Old Trafford from the United States, where he plays for Major League Soccer (MLS) club D.C. United.
Confirmation of a trial spell is expected to come later this week.
The Washington Post reported on Wednesday that Adu had been given permission by D.C. United to train with Manchester United for two weeks later this month.
Once seen as key to the future of the U.S. game, the Ghanaian-born forward became the youngest player to represent the U.S. senior team when he made his debut against Canada in a friendly in San Diego in January, aged 16.