Nemanja Vidic has warned his United team-mates that they will have to improve just to stand still.
A look at the players brought in over the summer by the Reds' Premier League rivals tells the defender that retaining the title will be a huge task.
"We need to improve everywhere. If you want to win the Premier League and get to the Champions League final, everyone has to take one step up," he said.
"We have to be better this season. If we play at the same standard as last season, we will not be good enough to win the league."
Vidic is excited at the quality of United's close-season signings, with Nani impressing in their pre-season games.
"Nani looks great," the defender said. "He's sharp and strong, he has a lot of stamina and he will be an important player for our team."