Jurgen Klopp insisted Vincent Kompany should have been shown a red card for his tackle on Mohamed Salah during Liverpool's trip to Manchester City on Thursday.
City claimed a potentially vital 2-1 win in the title race , as they moved back to within four points of the Reds at the top of the table.
Defeat would have left Pep Guardiola's men 10 points adrift of Klopp's side, and the Reds would surely have fancied their chances of emerging victorious had Kompany been dismissed in the first period.
The Belgian defender threw himself into a tackle on Salah to stop the Egyptian charging through on goal, with Kompany leaving the ground and never appearing to be in complete control. He was shown a yellow card for the incident, but Klopp was left confused as to how Kompany was not given his marching orders.
Speaking to Sky Sports, Klopp said: "I really like Vincent Kompany, but how on Earth is that not a red card?
"He is the last man and he goes in. If he hits Mo [Salah] more, he is out for the season. It is not easy for the ref and he may not see it how I see it."
Kompany, who said he had never witnessed a City performance like it, was convinced he made a good tackle, however, and never thought about letting Salah escape.
He added: "I thought it was a great challenge, was it not? I got the ball, a little bit of the man, but it wasn't naughty.
"I didn't try to injure him. It was that or let him go through on goal, and in my mind there was only one outcome."
As well as being disappointed at that decision, Klopp was also frustrated after he felt his side gave City a difficult evening in Manchester.
"If you think about which kind of goal Aguero scored - there is no angle," the Reds' boss added. "There is no angle and [he put it] under the roof. So nice goal and in similar situations we didn't score today, so that's it.
"But I thought everybody could see why we have the points we have. We were in the game, we were difficult to play."