The Gabon international made 87 appearances for the French outfit across a loan and permanent spell in Ligue 1, scoring 37 goals in that time.
His performances caught the eye of Dortmund and in July 2013 he penned a five-year deal at the Westfalenstadion.
However, the 25-year-old says he would like to return to ASSE at some point in the future.
"I still follow them, it's part of me. I'm happy with their season. Now, they have to keep going and push the big guns."