Sir Alex Ferguson criticised the "shocking" tackle by Chelsea's Ashley Cole on Javier Hernandez that could rule the striker out for two weeks.
The incident occurred late on in Manchester United's 3-1 win on Sunday.
United manager Ferguson told MUTV: "It was a shocking tackle. Ashley Cole is very reckless at times. Being committed, you can sometimes go over the edge a bit.
"We don't know how Hernandez will be. His leg is very numb."
Ferguson also questioned why, with the foul occurring in the area and Cole subsequently booked, a penalty was not awarded although referee Phil Dowd was seen to explain to the players that the ball had gone out of play moments before the incident.
Chelsea manager Andre Villas-Boas defended Cole and said the full-back might not have made the challenge on Hernandez if the officials had got earlier decisions correct.
After seeing two narrow offside decisions go against his team for United's first two goals, he felt the dynamic of the game had already been set.
"If it was 0-0 maybe Ashley is a little bit more mentally in control of the situation and doesn't do the red card foul that you mention," he said.
As well as potentially losing Hernandez, who was making only his second start of the season, United also face concerns over defender Chris Smalling who went off early with a groin injury. He could also be out for United's next two games, at Leeds in the League Cup on Tuesday and at Stoke in the Premier League on Saturday.
Ferguson told the club's website: "Smalling's got a groin injury so we'll see what it's like during the week."
After a frenetic game in which Chelsea had 20 shots to his side's 12, the United manager suggested the end-to-end nature of the game at Old Trafford made it seem like a game of basketball.
"It's hard to analyse as there were so many mistakes," he said.
"That made an exciting game. It was like basketball - you attack then we attack. It was so open for them."
Smalling opened the scoring, heading in unmarked from Ashley Young's free-kick.
Nani lashed home from 25 yards as defenders backed off, before Wayne Rooney made it 3-0 after the ball bounced to him following a Phil Jones run.
And Ferguson added: "Phil Jones is a marvellous young lad. Look at the third goal for instance. He wasn't going to lose the ball.
"He's been sensational since he came to us."
Ferguson was delighted with man-of-the-match Nani, who was playing in his 100th Premier League game.
The United manager said: "Nani's finish was sensational. Today we saw him at his very, very best.
"When we got the ball wide, they couldn't cope."
Fernando Torres made it 3-1 just 30 seconds into the second half - but missed an open goal after rounding David de Gea, Ferguson describing the fluff as "unbelievable".