Bale had been rested for the league win but is expected to feature in the starting lineup with Cristiano Ronaldo, who scored twice against Osasuna. Real are eyeing their 10th European crown and lead 1-0 from the first leg in Madrid last week.
"I feel good," said Bale. "I've had a few days training. I'm hoping to play tomorrow and looking forward to it.
"We are ready to give it 100%, our best shot. I don't feel like we've qualified for the final yet."
Real will need all their firepower to counter attack with pace as the Germans, who need to score twice, will likely dominate possession.
"We have a slight advantage from the first leg coming here but that is it," Carlo Ancelotti, the Madrid manager, said. "We know it is going to be very difficult. We are not that stupid as to think we have already qualified."
His counterpart, Pep Guardiola, is hoping Franck Ribery will rise to the occasion and inspire his side to a second-leg fightback.
"Franck played like he was possessed at the weekend [against Werder Bremen]," Guardiola said. "He fights and fights and for this reason the people love him here at the Allianz Arena.
"He is one of the best players in the history of Bayern Munich and we need his help."