Certain sections of the Bees support have expressed their displeasure at the Fulham youngster returning to Griffin Park.
Trotta cost Brentford automatic promotion on the final day of the 2012/13 campaign, as he crashed a stoppage-time penalty against the crossbar and could only watch in horror as Doncaster Rovers broke down the other end of the field to snatch a winner of their own - and the League One title.
Rosler is, however, eager to point out that the 20-year-old did a lot of good work for the club last season and should not be judged on one unfortunate incident.
He said: "It's important everyone gives Marcello a chance.
"He knows some people have not forgotten. Of course, people still remember him for that penalty.
"I remember the impact he made for the club. We should judge him on that.
"Marcello has come to fight for his place and play.
"I feel he is a good solution for us. He bounced back from that Doncaster game and I expect him to help us achieve our goal this season."