Inter Milan boss Leonardo feels Schalke will prove tough Champions League opponents.
Inter drew the Germans in Friday's quarterfinals lottery.
"No quarter-final at this level is going to be easy," said Leonardo.
"Schalke have a lot of enthusiasm and have grown after investments, year on year. They've done very well in the Bundesliga and qualified for this stage, with players like Raul and Jefferson Farfan."
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