The 21-year-old midfielder returned to his native Switzerland on a temporary deal with Luzern for the second half of the last campaign.
"There's a lot of competition in the squad, more so than when I first arrived, so it will be tough, but I'm ready," Kasami told the club's official website. "I want to play my part and help the team to a successful season.
"I don't think the fans have seen a lot of me in a Fulham shirt, so hopefully that will change this season. I think I'll get my chance, so it's up to me to impress and do well."
Fulham play their final pre-season fixture on Saturday when they host Italian side Parma at Craven Cottage.