Owen Coyle felt Nemanja Vidic was guilty of a 'terrible challenge' on Johan Elmander during Bolton Wanderers' 4-0 defeat by Manchester United.
Vidic caught Elmander with an elbow midway through the second half of the game at the Reebok Stadium as the duo challenged for a ball on the edge of the penalty area.
The incident was not penalised by referee Martin Atkinson and it left Trotters striker Elmander requiring five stitches in a head wound.
The Swede was later substituted and Bolton manager Coyle was not happy that the challenge from Vidic passed without punishment.
"I can only assume the referee has not seen it," said Coyle.
"Vidic has caught him with an elbow. There was blood pouring out of it.
"I am not looking for excuses, but anyone who has seen it knows it was a terrible challenge."
Bolton had gifted United a first-half lead when Jlloyd Samuel side-footed Ryan Giggs' low cross into his own net and Coyle acknowledged the full-back was feeling down after his mistake.
He added: "Jlloyd cannot feel any worse.
"Next time he may make a better decision. It was a nice ball in from Ryan Giggs, but no more than that."
Dimitar Berbatov later scored twice and Darron Gibson weighed in with the fourth goal for United, but Coyle felt his team contributed to their own downfall.
"I'm disappointed with the defeat and the manner of the defeat late on," said Coyle. "That's what happens when you play against the best teams. If you switch off and gift them goals as we did you're going to be punished.
"But for 70 minutes of the game I thought we were terrific.
"There was a lot of things we could have done better. The scoreline flatters Manchester United - no doubt about it.
"We were the architects of our own downfall."