"I have not come here just to sit in the stands," he told a news conference on Tuesday. "I am here so that's a good sign and I feel fit enough to play."
Robben, whose goal against Fiorentina sent Bayern into the quarter-finals, missed the first leg with a calf injury but coach Louis van Gaal said on Monday he hoped the winger would have recovered for the match at Old Trafford.
Bayern fought back from a goal down in the first leg to win 2-1 but their Dutch coach believes United will be a tough proposition on home soil.
"Yes," was Van Gaal's simple response when asked if United would be the favourites to progress.
"We have lots of confidence and we come here with 19 fit players and that is a great situation to be in.
"United are a top team, they have a great squad with experienced players.
"I think the atmosphere will be super, it always is when you play in England.
"They have an away goal so that makes it tough but I'm sure we will be challenging tomorrow."
CHALLENGING EVENING
Bayern captain Mark van Bommel agreed United will be confident of winning even though their talismanic striker Wayne Rooney was struggling with an ankle injury.
The England forward, who has 34 goals in all competitions this season, was injured in the first leg last week.
Dutchman Van Bommel, unaware Rooney had already been ruled out by United manager Alex Ferguson, said he would have liked him to play and expected a challenging evening at Old Trafford.
"I hope that he will play but Manchester United do not consist just of Wayne Rooney, they have a lot of other very good players," he told reporters.
"We will give it our best shot, with or without Wayne Rooney.
"We are leading 2-1 but I think United are still the favourites... they are at home and I think they are the favourites along with Barcelona to win the title."
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