Sir Alex Ferguson has criticised David Luiz's professionalism, claiming the Chelsea player's "dying swan" act got fellow Brazilian Rafael sent off at Old Trafford.
Rafael became the first Manchester United player to be dismissed in the Premier League this season during the final minute of his side's 1-0 defeat.
After Luiz twice nearly caught Rafael with what Ferguson felt was an elbow, Rafael lashed out, prompting referee Howard Webb to brandish a red card that will trigger an automatic three-match ban and end the full-back's season.
However, Ferguson felt Luiz contributed to Rafael's punishment by rolling around on the floor in apparent agony, but with a wide smile on his face.
"Rafael retaliates but he Luiz quite clearly elbows him twice then rolls about like a dying swan," said Ferguson.
"He was smiling too. That is bad. It's not very professional."
Speaking on MUTV, former United defender David May said: "It is a joke. Players are cheating. It is disgusting."
The incident came not long after Juan Mata's deflected shot beat Anders Lindegaard for what turned out to be the winner.
It meant United failed to score in a Premier League game on home soil for the first time in 67 matches.
And, other than the Rafael incident, Ferguson had no complaints given the lacklustre nature of his side's performance.
"I am disappointed," he said. "It looked like we had put the tools away. Maybe it was (because their job is done). That has a lot to do with it.
"It has been a long season and the final big effort was last week against Arsenal. But there was no edge to our game. Chelsea were the better team."
Wayne Rooney felt he had been fouled by Ramires at the start of the move that led to Chelsea's 87th-minute winner, although Ferguson was not so sure.
"I don't think Wayne was fouled," he said. "But the referee was giving us nothing anyway. The goal was a bit lucky because it deflected off Phil Jones. When that happened so late in the game there was not a lot we could do about it."