After consecutive home defeats in the Premier League, United scraped past Shakhtar Donetsk on Tuesday in the Champions League thanks to a 62nd-minute Phil Jones goal - a victory which cemented top spot in A.
It was a far from convincing display, however, and Keane singled out veteran centre-back Ferdinand and the out-of-sorts Ashley Young as high-profile players guilty of letting down their under-fire manager.
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"You can defend players for making mistakes but you cannot defend players for not tackling and not getting close to people.
"[United] had a couple of good chances through Ashley Young towards the end of the first half. He should certainly hit the target. I think it sums up his time at Man United: Just not good enough.
"David Moyes took the heat off the players before the game by saying it is his responsibility but we are talking about experienced players.
"Rio Ferdinand's decision-making, the chances he has taken, it is ridiculous. It [was] like his debut.
"As we said before the game, there are big question marks over the manager and the players. That, for Manchester United, is certainly not good enough."