Robben, who is winning his battle to be fit for the game after missing the first leg with a calf problem, believes Bayern can pile the pressure on United with an away goal.
"The pressure is massively on the shoulders of the United players," Robben told the Daily Star. "They know all we need is one goal and the game could be over.
"They would find it almost impossible to come back from that.
"We have already shown we can beat the English team and we are confident we can do it again."