Freddy Adu, who flopped as a teen prodigy in Major League Soccer and with the United States national team, returned to the US league on Friday on a free transfer from Portugal's Benfica. Adu will join the Philadelphia Union, whose executive vice president of soccer operations is Peter Nowak, who coached a 14-year-old Adu in his MLS debut with DC United in 2004 as the youngest US pro athlete in 115 years. United won the MLS title that season, Adu contributing five goals and setting up three others. Adu later played under Nowak for the American team at the 2008 Beijing Olympics. The attacking midfielder, now 22, has spent the past four years touring European clubs trying to find a fit with no success. Adu's star brightened in June as part of the US Gold Cup squad. He assisted on both American goals in a 4-2 loss to Mexico in the regional tournament's championship match. He was on the US roster, although he did not play, for Jurgen Klinsmann's debut as coach of the American national squad two days ago in Philadelphia, a 1-1 draw in a friendly with Mexico. After three seasons with DC United, Adu played briefly for Real Salt Lake before his rights were obtained by Benfica. Adu cracked the Portuguese club's starting lineup for 11 matches, scoring twice. A series of loans followed, first to French club AS Monaco, then Portugal's Os Belenenses, Greek side Aris and Turkey's Caykur Rizespor.