The former Manchester United forward scored 17 times for the Werkself in the Bundesliga last season, but his return of five in 15 games so far this term has disappointed Voller.

"I expect a lot more from Chicharito," Voller told the Bild newspaper prior to Leverkusen's departure for Orlando, where they will spend the next nine days in a training camp.

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"He knows himself that he has to raise his game. I think he is the first to be unhappy with his first half of the season."

Voller, though, is not entertaining the idea of selling the Mexican: "I cannot imagine that," he said. "We just need a good, functioning Chicharito."

Hernandez's five goals still make him Leverkusen's top goalscorer this season, with Roger Schmidt's men lying ninth in the Bundesliga over the winter break, six points adrift of the top six and European qualification.

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