"When you are permanently injured, physicality is very difficult to get. Then there are qualities that a player has or doesn't have.
"You cannot improve or make them have. I will give you an example. Robertson, Mané, Salah, Wijnaldum, Keita, Fabinho. They are physical players, and on top of that, they are good players technically.
"I also have lot of good players technically but we don't have lots of players with that intensity, that physicality, so when the game has high levels of intensity, it is difficult for us."
Mourinho, who lost Chris Smalling to an injury during the warm-up, suggested his United squad lack players with the characteristics not only of Liverpool, but his most successful teams at previous clubs.
"You can compare my Porto team with Liverpool," he said.
"They are fast, they are intense, they are aggressive, they are physical, they have an objective. They play 200 miles per hour with and without the ball. I am still tired just looking at Robertson. He makes 100m sprints per minute, absolutely incredible.
"You can compare [with Porto]. The qualities of the players are there. It was my best team in defensive transition. We lose the ball and we bite like mad dogs and recover the ball after a few seconds. In Real Madrid, I had my best team in direct counter-attack because I had a young Di María, young Ronaldo, young Higuaín and young Benzema, and in Inter, I had my best team in a defensive low block. You can be there for five hours and you don't concede a goal. Players make teams play in a certain way."
Asked why he had not corrected his squad's flaws in four transfer windows, Mourinho said: "I don't think a football team is just a squad. It is much more than a squad and I repeat I am really, really happy with the players I had on the pitch with their effort, with their attitude."
Manchester United's legends working as pundits were damning of their former club's showing.
"Liverpool were streets ahead," said Gary Neville. "Not one of them can actually receive the ball and pass the ball or take the ball. I just find it absolutely staggering. United were awful to be honest. The only team you thought were going to win the game were Liverpool. In the end, you couldn't complain about the result as a Unted fan. It's not good enough."
Roy Keane said the lack of quality was obvious.
"I certainly believe a lot of the players playing for United [against Liverpool] aren't good enough for Man United. I think they are good players, but not for Man United," said Keane. "The biggest problem is defensively. You have to get some sort of foundation to go forward. You have got to keep some clean sheets. They look like they are all over the place. Liverpool were toying with them.
"I know people say they have already spent money on some defenders, but they have not been good enough. Go buy some more. You are Man United, huge club.
"The scary bit is when you listen to the manager and he is talking about finishing fourth. Manchester United. That's where they are at.
"If you came from the moon today and you did not know anything about Man United, you'd say they're an average Premiership team."
