The Netherlands international believes Real Madrid boasts "the best players" and is the most dangerous opponent left in the Champions League.
The reigning European champion has been odds-on to become the first team to defend the trophy in the modern era throughout the tournament so far, but Robben believes such expectation counts for nothing against a side he believes is the most dangerous in the competition.
"They have the best players," Robben told Kicker. "If you have a 10 minute period where you switch off, you can suddenly concede three goals. There'll be a lot demanded of us.
"We are no longer favorites. Of course we want to win the Champions League again, but we're in the semifinal – and anything can happen. Real are the most dangerous opponent we could have faced."