Ashley Young said Manchester United lacked intensity against Derby as they went out of the Carabao Cup to the Championship side on penalties at Old Trafford.
Manager Jose Mourinho had used his programme notes to issue a warning to his players following the weekend draw with Wolves that "95 percent isn't enough when others give 101 percent."
But after the penalty shootout defeat, defender Young told MUTV: "I think they had more intensity than we did.
"When you play these games, you have to show that intensity and go further than the opposition. We didn't do that and I think we got punished. They won the game."
It is not the first time the attitude of United's players has been questioned this season.
Paul Pogba, who has been stripped of the vice-captaincy by Mourinho, said Brighton had "more hunger" during United's defeat at the Amex Stadium last month.
And following the draw with Wolves, Mourinho criticised his players' failure to match the visitors' commitment.
"They play like I like to play, which is like the World Cup final," he said. "That is the attitude I like my teams to have in every match. We didn't have that."
In his programme notes for the Derby game, Mourinho wrote: "I hope we can look back on Saturday's game against Wolves for an important lesson; a lesson that I repeat week after week after week, a lesson that some boys are not learning: every team that play Manchester United are playing the game of their lives and we need to match that level of aggression, motivation and desire."
United travel to West Ham on Saturday, with Manuel Pellegrini's side having bounced back from a poor start to the season to record a 3-1 win at Everton and a 0-0 draw with Chelsea in their last two matches.
"When you lose a game and when you a draw a game, you want a game as quick as possible to get back to winning ways," Young said.
"Saturday is another day, another game, and we'll look to go to West Ham and get the three points."