Granero has issued a rallying cry to his team-mates to reproduce the form which earned vital points against Chelsea, Tottenham and champions Manchester City as the R's attempt to cause an upset against Sir Alex Ferguson's side.
"They are a very good team," Granero told the Fulham Chronicle.
"When we played there we did a good job, even though we lost 3-1. On our pitch they will suffer more because it's much smaller, so we will have our chances.
"We have to repeat the work rate we showed against Chelsea, Spurs and Man City and then take a step forward and try to create chances because we're a good team.
"We're still confident we can get out of it but are running out of games. Every week that passes is another less so we need to start winning, no matter who we're playing against.
"It is a final for us. We won't give up."