Former Argentina international Mario Kempes claimed on Monday that Messi's level 'had dropped' for Barcelona recently but Emery is not buying it ahead of their Copa del Rey semi-final second-leg at Camp Nou.

"He is the best player in the world, I do not believe he is in a bad run of form," Emery told reporters at a press conference.

The Spanish coach then demanded full focus from his men ahead of Wednesday's clash.

"This match symbolises opportunity and hope for Valencia and we have the responsibility to work hard for those things," he said.

"Our preparation for this match is based on nullifying everything we know about Barca and take full advantage of our virtues."

"Barca always prepare for their matches against us well. Little details can make a big difference in the final score."

The Catalan club hold a slight advantage after a 1-1 draw in the first leg at Mestalla.