In August 2016, the Berlin-born became only the sixth player in history to score in all four leagues, having struck for Hertha Berlin and Schalke 04 in Germany, Portsmouth in England, AC Milan in Italy and Las Palmas in Spain.
"I want to play at a good level for as long as possible and just stay healthy," he is quoted as saying by ESPN.
"To win trophies? I've never been a trophy guy. I would love to win the Champions League one day, but I am being realistic that I now most likely won't win it. Fine with me.
"My dream is to help young players. I don't want them to make the mistakes I did in the past. The rest? I was 20 when I dreamt of other things.
"If I had always been honest to myself, I might play at Real Madrid."
In England, he won the League Cup with Portsmouth but his best time was in Italy where he claimed Serie A and Super Cup titles with Milan.
The midfielder also played at the 2010 and 2014 Fifa World Cup tournaments for Ghana.