The centre-half has fallen down the pecking order at Old Trafford.
Phil Jones and Eric Bailly have started the new season as Mourinho’s preferred pairing at the back.
Meanwhile, summer signing Victor Lindelof, Daley Blind and Marcos Rojo are also options in the middle of defence.
As a result, Leicester are looking to swoop for the 27-year-old.
According to the Mirror, Foxes manager Craig Shakespeare is keen on Smalling.
The England international has plenty of experience to offer Leicester.
And Smalling would be lined up to partner Harry Maguire at the King Power Stadium.
The Mirror add Smalling can leave Old Trafford before Thursday’s 11pm deadline.
And after United’s 2-0 Premier League win over Leicester yesterday, Mourinho revealed he is not set to make any more signings.
“Everyone knows I would like a fourth player and I cannot hide that because I had that in my mind,” Mourinho said.
“But I am happy if I am not going to have that and I don’t think I am going to have that.
“I was the first to tell my board not to feel any kind of pressure from me in that respect.
“Probably next summer, I will have to try and get a player from a position I think can make us stronger.”
Even though United are ready to offload Smalling, it seems Mourinho would be happy with his remaining squad.
