Adu admits he played hurt. The team signed him to a multiyear contract, one that last season paid him nearly $600,000, so the expectations were high.
Now, with the injury behind him, Adu understands it is time for him to produce.
"Now I am healthy, fit, happy, and I am playing at a pretty decent level now, and happy with my level of play, and I have to bring it to help this team out," Adu said after Thursday's practice at PPL Park. "This team did pay a lot of money to get me here and, obviously, I need to get out there and help the team get wins."
This year Adu has appeared in just one game, starting the opener and playing 74 minutes in a 3-1 loss to the Timbers at Portland on March 12.
After that he left for duty with the U.S. under-23s. He was the captain of the team and played well, but the U.S. was eliminated after a 3-3 draw with El Salvador in an Olympic qualifier.
In four games, which included an international friendly with Mexico, Adu had one goal and three assists to lead the U.S. team with five points. It was a bittersweet time, since he performed well but his team didn't qualify for the Olympics.
"That was probably the worst moment of my career so far, just not being able to qualify for the Olympics, because it means too much to me personally. But I told myself afterward I will not let myself feel that way ever again," Adu said. "I will keep working harder and harder to a point where I don't feel that way."
Adu is so important for a goal-hungry team such as the Union because he the rare ability to break down defenders one-on-one.
"That is exactly what I will try to do," he said. "We're a good team and keep the ball pretty well, but when we are closer to the goal, we are going to need people to break people down, break the defense down and take people on."
While Adu and his U.S. teammates are bitterly disappointed not to be competing in the London Olympics, this is now the time for him to make his mark on the Union.
It's hard to believe that he won't turn 23 until June 2, but Adu has been a professional since the age of 14, and this is the age where he should be reaching his peak.
Most of all, he will be able to concentrate on the Union and Major League Soccer for the rest of this season.
"I am really looking forward to this and I am excited and happy," he said. "My teammates are great and I enjoy playing with them."
And no doubt, they should also enjoy playing with Adu. The team desperately needs a difference-maker, and a healthy and hungry Adu can definitely fit that bill.
Contact Marc Narducci at 856-779-3225 or mnarducci@phillynews.com, or follow on Twitter @sjnard.