The Italy Under-19 international will be making his second loan move to Griffin Park after spending six months there last season.
Trotta, who will stay until January 5, netted nine goals in 29 appearances for the Bees, but the 20-year-old will be remembered by many as having missed the last-gasp penalty against Doncaster which would have sent Brentford into the Championship.
Brentford Manager Uwe Rosler told the club's official website: "It is human nature to think that the glass is half empty and maybe remembering the things which weren't working out.
"I remember he joined us on November 24 and he then played every single game for us when we were unbeaten in 10 and won seven out of 10.
"He is still very young and he learned a lot last year."
Trotta, who has also been on loan at Watford and Wycombe, has made three substitute appearances for Fulham.