The Swiss midfielder was set to complete a move to the Italian club before the window closed on Thursday but his international clearance papers did not go through on time due to a failed wi-fi connection at a Milan hotel.
Kasimi, who signed for Fulham in 2011, has made just eight appearances for the Cottagers.
The 20-year-old's agent Mino Raiola was left fuming by the mishap and pointed the finger of blame at the earlier closing of the transfer window in Italy.
"It's ridiculous that the internet connection has not been working correctly,” Raiola told Sky Italia.
"We completed all the documents before the deadline but we don't know if they arrived in time.
“It was set up for transportation via the internet and the documents were compiled and sent for Kasami to Pescara and we insist in repeating that everything was done in the right way.
“We hope that the league will give consent to this transfer and why, for example, does abroad close late and we do not? This is bad for the Italian transfer market and the rules should be changed.”