Dortmund have been Bayern's closest rivals in the past five Bundesliga seasons – winning two titles of their own – but find themselves bottom of the table in the current campaign.
Having lost Robert Lewandowski to Bayern at the end of last season, Dortmund's attempts to replace the Pole's firepower have failed with Ciro Immobile and Adrian Ramos scoring five goals between them so far.
"I like Klopp and Dortmund," said the Spaniard. "They have great players, but now they are bottom.
"We have to watch it [their fall], that could happen to us."
"If we understand that we can lose tomorrow, then we are on the right track," he added.
"Schalke are one of the best teams in Germany. It is difficult to attack them, we must patiently play.
"They will be super organised defensively."
