The Italian, who was in charge of the Three Lions from 2007 to 2012, watched Jose Mourinho's side lift the Europa League on Wednesday, but was less than impressed with what he saw on the pitch.
"It was a poor game," Capello told the Daily Star. "There was not enough exciting football.
"United are strong and defend well, which is good. But they are not an exciting team."
The Europa League win sees United automatically qualify for the Champions League, which should allow them to attract a higher calibre of player to the club, with Mourinho likely to add to his squad in over the close-season.
However, Capello does not believe that the signing of the 26-year-old will be enough for Mourinho's side to properly mount a bid for the Premier League title.
"Griezmann is a very good player. But what is his best position? He is not a striker. United need more than him," Capello continued.
"They have other areas in which to strengthen. Chelsea are so strong and they need to catch them. It will be difficult."