The former Bayern Munich midfielder spoke positively of the 23-year-old, who justified Joachim Low's faith in him with a goal against the Ethniki
The 23-year-old made his tournament debut, and was one of the more livelier players in Gdansk, scoring the fourth goal as Joachim Low's men cruised into the last four of the tournament.
And Ballack, who won 98 caps for his country across an 11-year period, admitted that he was impressed with Reus, along with Germany's other young stars.
"He was really good and is a great option for the next game. It's nice to see that the young players come onto the pitch and take their chance," the 35-year-old told ESPN.
"And above all, Reus was really good."
Germany encounter the winner of the England-Italy quarter-final in the last four on Thursday in Warsaw.