I don't think so. The performance was very poor, but we won't perform that bad on Sunday, considering how many changes will be made to the team. This just told me that our (mostly) second-string team can't win away to decent teams in Europe - that's how it would be with most clubs, in fairness.
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I do think there is a big overreaction in this thread. We played Man City 5 days ago, in which Mourinho would have played more or less our strongest team possible. He made 8 changes out of 10 outfield players today, so it obviously wasn't our best side. I think most CL teams would struggle away to Feyenoord if they put out a side that had 8 changes from their squad on the weekend, assuming they weren't resting players (like Barca, for example).