Wenger feels Barca have lost their unity this season.
"Since the beginning of the season, Barcelona in the Champions League has been worrying. There is something that has disappeared, in terms of the trust and collective momentum. I've always been a big fan of this form of solidarity that is inside Barca.
"It is not there at this moment," Wenger told Eurosport.
"The Achilles heel is the defence. They cannot defend at set pieces."
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