The 20 year-old midfielder has joined Lyon on-loan for the rest of this season with the option of the move being made permanent in June.
Crosas said: "The truth is that I have had seven seasons with the Blaugrana and while it is hard for me to go, the world does not finish here, at Barca. In addition, I leave with the intention to return. That is my objective.
"I want to prove I am capable of playing for Barca. But I am joining Lyon with the only focus on being successful with my new team. They deserve that for showing faith in me."