The Fulham striker, 20, disobeyed orders not to take a stoppage-time penalty against Doncaster at the end of last season - and crashed his spot-kick against the bar.
Doncaster then went back up the other end and scored the goal that clinched promotion for the Yorkshire club.
Now some Brentford fans have bombarded social media sites to question his return.
Impact But Brentford boss Rosler 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."
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