The Brazil international will join the Catalan outfit on a five-month loan deal.
"I've come here to pick up my stuff and say goodbye to everyone," Coutinho said on Monday to Sky Sport Italia.
"However, I will only be away for five months.
"I need to play and I think I can do well at Espanyol before returning here.
"I would like to thank all of the fans but I will be back. I'm an Inter supporter myself and I think we can win the league this season."
The 19-year-old moved to Inter in the summer of 2010 from Vasco Da Gama.
Coutinho has scored one goal in five league appearances for Inter this season.