This is kind of a shit argument though. KDB, Silva, Aguero have all managed to massively up their defensive work rate for Pep.
So even if it was true that he was expected to defensive work - which IMO it isn't, he's expected to just do normal winger tracking back and mostly defend by pushing the fullback backwards - just saying "Oh well he didn't defend" isn't really good enough.
Because if Sané can't be bothered to defend or learn to defend, he can just sit on the bench while Danilo or Mendy play that role. He's not going to play in the front 2, where Aguero, Jesus and Sterling are ahead of him, so either he needs to do what dozens of other players before him have done for Pep, or get used to only playing when we go 433/4141.
Also it was barely 20 minutes in that Pep put Kompany on that side, so he had the benefit of our best defender inside him, and Fernandinho was clearly giving him extra help too. He was up against Mason Holgate, a CB out of position with almost 0 experience, he shouldn't have been outplayed even as a winger being asked to play as a very attacking wing back.
Plus he was even really poor when he went to play his normal position, and got hauled off.
Perhaps he just had a shite game? Perhaps he's part of the problem and not completely blameless as many people seem to want to think.