Adu played the second half in a 1-0 win over Offenbach in an exhibition in Ingolstadt’s winter training camp in Turkey.
Ingolstadt is next-to-last in the second division, Ingolstadt coach Benno Moehlmann says he wants to observe Adu for the next few days before making a decision whether to keep him.
Adu joined Benfica in 2007. He has made 11 appearances for the Portuguese club and been loaned out to French club Monaco, Belenenses in Portugal and Aris in Greece. In July, Swiss club Sion declined to sign Adu after a week’s training.
The 21-year-old forward was not selected to play for the U.S. at the 2010 World Cup. He has struggled to fulfill the potential he showed when he joined D.C. United at age 14.