Gary Neville singled out Manchester City midfielder Yaya Toure for fierce criticism following his side's comprehensive 4-2 derby defeat at Old Trafford on Sunday.
Toure was in a City midfield which was overrun by United, with the likes of Michael Carrick and Marouane Fellaini dominating the Ivorian and his teammates.
Toure's powerful displays have been key to City's success in recent seasons, but Neville said the 31-year-old had become a liability against top sides.
"He can't play in a two in midfield against any team of quality," the former United full-back said on Sky Sports 1.
He added: "Before the game, I asked, 'Is Yaya Toure able to match Fellaini in that pocket?' He didn't. He paid no attention to him at all. It was a complete dereliction of duty.
"Vincent Kompany nearly got sent off when he came out into that space and they gave the third goal away [to Juan Mata] with Martin Demichelis stepping into that space, leaving a gap between Pablo Zabaleta and Eliaquim Mangala.
"There is too much evidence he cannot do his job in the big matches."
City boss Manuel Pellegrini, though, defended the midfielder and said his players had to gamble more after finding themselves 2-1 down at the break.
"Fellaini's in a good moment but Yaya marked him very well in the first half," he said on his club's official website. "After that we had to take more risks and they had space. Finally they won the game.
He added: "I don't think it was a problem of pace or the United team -- it was our own mistakes on at least two goals. We had a lot chances at the start of the game to score another goal.
"It's not easy to play with more pace and trust when you're two goals down and they have more of the ball."