The goalkeeper expects the Catalans to put up a fight in the return leg in Catalunya and believes the ballboys could even play a part in the outcome at Camp Nou
The Bundesliga champions will be confident of holding off their opponents after their 4-0 first-leg win at the Allianz Arena last week, but the former Schalke keeper has stressed that the Catalans cannot be written off entirely just yet.
"We have to invest everything to avoid a catastrophe. They're wounded but they'll still do everything they can to make the final. They'll put us under incredible pressure," he told the club's official website.
The shot-stopper previously played at Camp Nou with Schalke in 2007-08 and he has not forgotten about the atmosphere and the behaviour of the ballboys five years ago.
"I remember the special atmosphere and how the ballboys reacted to Barcelona taking the lead. They stopped throwing the balls back onto the pitch. I kept coming close to a yellow card, because it made me so mad.
"So it could be that the balls fly back onto the pitch very quickly on Wednesday."