United face Tottenham on the weekend.
"The quality has improved," he said. "We saw last season how competitive the league is and it's been even more so this year.
"Sides such as Tottenham and Manchester City have raised their games, whilst other teams understand they have to improve if they want to stay in the league because it is so competitive. They have done that.
"It is a physically strong league and players have raised their game in that way too."