Sir Alex Ferguson admitted Ashley Cole's "shocking" tackle on Javier Hernandez had taken the shine off Manchester United's 3-1 win over title rivals Chelsea on Sunday.
Ferguson saw United storm into a three-goal lead through Chris Smalling, Nani and Wayne Rooney as the champions maintained their perfect start to the Premier League campaign.
United are two points clear of second placed Manchester City, but Ferguson was more concerned with drawing attention to Cole's late tackle on Hernandez in the penalty area in the 79th minute.
Chelsea left-back Cole was booked for catching Hernandez with a nasty two-footed challenge, although no penalty was awarded as the ball had gone out of play, and the Mexican striker was forced to come off with an injury that could keep him out for at least two weeks.
"For me it's a shocking tackle. The referee has booked him (Cole) and if he's booked him I don't know why it wasn't a penalty," Ferguson said.
"We're going to have to wait until the morning because at the moment his leg is very numb. He could be out for a couple of weeks anyway."
Although Ferguson was delighted to see off a title rival, the Scot conceded that United had been slightly flattered by the margin of victory as they allowed Chelsea far too many chances with some careless passing.
"It was a fantastic, open match but we created our own problems for ourselves," he said.
"We gave the ball away in attacking areas and they kept counter-attacking us. In the first half they could have scored two or three.
"We created more opportunities, fantastic opportunities, particularly through Nani and Ashley Young, who kept getting in very good areas. That was our strength, they couldn't cope with that."
Chelsea manager Andre Villas-Boas, beaten in a league match for the first time since April 2010, insisted his side deserved more for their performance and he took heart from the way they put United under pressure in the second half.
"It was a strange game, very, very open and a lot of opportunities for both teams." he said.
"If luck could play a better part for our side today, maybe. We had some very good chances to even the score or even to score first.
"The scoreline went crazy in the first half, but we had good opportunities to do something in this game.
"Coming back from 3-0 down is always difficult and we had to take risks without exposing ourselves too much.
"The second-half recovery was very good and we had a couple of chances to even the score. The scoreline is crazy."