The 18-year-old will undergo a medical at Benfica before he can complete a move to the Estadio Da Luz.

Adu was the youngest ever player to represent USA, as the Ghanaian-born forward wore the Yanks' shirts at the age of 16.

The U-20 US captain also led the youth team to reaching the quarter-finals of the 2007 U-20 World Cup in Canada this summer.