United are now 19 points behind Liverpool following their 3-1 defeat at Anfield on Sunday and are facing a huge battle to secure a top-four place this season.
United were under pressure for large parts of the game and Mourinho conceded that his players struggled to match Liverpools fast start to the match.
But Mourinho also singled out Andrew Robertson, Sadio Mane, Mohamed Salah, Georginio Wijnaldum, Naby Keita and Fabinho as players who United are unable to match when it comes to intensity.
First of all, we have lots of problems related to physicality, we have lots of players that I could consider injury problems, because some of our players are always injured and is not with me, it was before me, Mourinho said after the game.
If you look to the stats with Mr Van Gaal and before Mr Van Gaal with David [Moyes], if you look to that period you have players that are permanently injured.
When you are permanently injured, physicality is very difficult to get.
Then there are qualities that a player has or doesnt have. You cannot improve, you cannot make them have.
I give you an example – Robertson, Mane, Salah, Wijnaldum, Keita, Fabinho – they are physical players, on top of that they are good players technically, I also have lots of good players technically,
But we do not have many players with that intensity or with that physicality.
So when the game has high levels of intensity is difficult for us.
Our first 20 minutes was difficult for us, then when we had the ball and the tension went down, when the intensity went down, it was easier for us to be in the game, we manage to have the ball and bring the game into, I would say, our side in the sense of now we are playing in the way we can. And these are our qualities.
And I think you like to say sometimes its the managers choice. You can compare my Porto team with Liverpool, because the qualities of the players are there.
It was my best team in defensive transition. We lose the ball, we bite like mad dogs and recover the ball after two seconds.
In Real Madrid I had my best team in direct counter attack because I had young [Angel] Di Maria, young [Cristiano] Ronaldo, young [Gonzalo] Higuain and young [Karim] Benzema, we killed everyone in offensive transition.
In Inter I had my best defensive team in a defensive low block, where people like [Marco] Materazzi, [Walter] Samuel, Lucio, [Ivan] Cordoba, in a low block you can be there five hours and you do not concede a goal.
Players make teams play in a certain way.
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