Fanni believes that his side were not good enough to get a result from the game but feels that the scoreline flattered Dortmund.
"It's fair to say Dortmund deserved the victory, but in my opinion the 3-0 scoreline doesn't really reflect the balance of play," Fanni told reporters. "There you go. Football can be cruel sometimes, but we'll learn from this and there are positives to take from the match.
"They were very strong on the counterattack. Those are the details which can prove decisive, as we saw for their first goal. After going behind it was always going to be tough to take anything from the game. We gave our all but unfortunately it wasn't enough. Hopefully things will turn out differently in the return match."
Marseille are in Ligue 1 action on Sunday when they face Paris Saint-Germain.