The Cherries won 3-0 at Old Trafford on Saturday.
"I think the performances have been as bad as this, but they've got away with it," he said. "They improved against Chelsea because they didn't have to take the game to the opposition. They could play counter-attack football.
"There's nothing wrong with being a counter-attacking side but when a team wants to sit back, you have to find a way of opening them up. They are devoid of anyone with any imagination or creativity apart from Bruno.
"Credit to Bournemouth. They had a game plan and pounced on it and were clinical in their finishing. But very rarely was I off my chair thinking Manchester United must score here. Bournemouth were quite comfortable.
"We're talking about a team in 16th going away from home to Old Trafford. I'm within my rights to think Manchester United, with world-class players and the money they've spent, should be able to break them down and score.
"But they got worse. In the second half, they came out and it looked like they had thrown the towel in, which is unfortunate for their fans watching on."