Sir Alex Ferguson was disappointed with the referee's decision to award the free-kick that led to Steven Gerrard's goal in the 1-1 draw at Anfield.
Rio Ferdinand tangled with Charlie Adam in the 68th minute but Ferguson also criticised Luis Suarez.
He said: "The referee is under tremendous pressure but, when you see it again, it was a very soft one.
"Suarez dives all over the place and it makes it very difficult for the referee," added Ferguson.
The United chief had earlier left striker Wayne Rooney on the bench following his sending off for England against Montenegro which resulted in a three-match Euro 2012 ban.
Ferguson added: "He's obviously had a bad week with England. He was very disappointed to be sent off and the three-match ban from Uefa makes it very difficult for England.
"He could miss all the European Championship. I wanted to have Wayne in the right state of mind.
"It's important to get everyone in good fettle and in good form. You don't want any albatrosses hanging over their heads."
Liverpool and England midfielder Gerrard believes Wayne Rooney "has to go" to next summer's Euro 2012 finals, irrespective of whether the Uefa punishment is reduced or not.
Gerrard said: "For me he has got to go, the talent that he is. He is that good a player, I think you have to take the risk and take him.
"We will have to see who we come up against in the group games but we should progress from the group stages and then you need your best player out there with you to push on all the way to the final.
"It is devastating he is out for the first three games. It is a massive blow for everyone."
Gerrard's goal against Manchester United was cancelled out by Javier Hernandez. On United's equaliser, Ferguson said: "I thought Hernandez took his goal brilliantly. He has such a great record and you always think he can score. I thought he was being man-handled by the Liverpool lads when he scored.
"It wasn't a game until the goals were scored. After that it became a much better game.
"It's always intense at Anfield and Liverpool always make it difficult for you. We have faced most of the top sides now but we won't know until the end of the season whether it's a great point to have taken home with us.
"Liverpool probably had the best chances to win the game but David de Gea made two great saves."