Fulham were prepared to let the Switzerland U21 international return to Italy on Thursday but the transfer documents arrived at Italian league offices 13 minutes after the window had closed.
"We have been told that the documentation arrived late," said Pescara chief executive Danilo Iannascoli.
"There has been a fax exchange with the English side, but the League answer has been negative.
"We believed that, with this being a foreign transfer, things could be done differently.
"We are disappointed because we had high hopes for this purchase."