The deal for Coutinho, 20, is reported to be worth around 8.5 million pounds ($13.4 million).
The former Brazil youth international moved on loan from Inter to La Liga's Espanyol last year having joined the Italian giants from Vasco de Gama in 2010.
Coutinho has scored twice in the Europa League this season for Inter and has made 47 appearances for the three-times European champions.
($1 = 0.6327 British pounds)
