Jose Mourinho accepts Manchester United must do better but feels it is unfair to compare the current side with the glory eras of the past.
United visit Southampton on Saturday in seventh place in the Premier League, 14 points behind leaders Manchester City and seven off fourth-placed Chelsea.
He says the game has “changed” so dramatically that it is impossible to repeat what has gone before.
“It’s more difficult to buy players of a high level,” said Mourinho.
“Before the smaller clubs were almost begging the big clubs: ‘Get my best players. I need to sell.’
“I know absolutely we have to do better. But one thing is to do better. Another is to compare ourselves with what Manchester United was in the past because it is impossible.”