Mourinho would not normally call on players after only a few days training but is set to be without six first-team players for Friday’s game.
Ander Herrera, new signing Diogo Dalot and captain Antonio Valencia are among the list of United absentees.
Asked which players would be unavailable against Leicester, Mourinho said: “[Sergio] Romero, he had a surgery after his injury. [Antonio] Valencia, he was injured in pre-season. Marcos Rojo, he was injured in the World Cup. Dalot had a surgery in Porto by the end of April and not yet ready.
“Ander Herrera injured against Bayern, [Nemanja] Matic injured in the World Cup and surgery in Philly, a couple of weeks ago. I think that's it.”
On the players who returned to training this week, Mourinho added: “They return on Monday, train tomorrow and today so you can imagine that they are not really fit and ready but we have needs. The list that I gave you before of the injured players is an important list.
“Today after training I will speak with that group of players [those returning from the World Cup] because everybody is different physically and mentally, to see how they feel, and to understand and to think how they can help or not help.”
Romelu Lukaku, Marcus Rashford and Phil Jones all progressed to the latter stages of the World Cup but cut their close-season breaks short to return to training.
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