Lukaku has failed to score in his last 10 games for Manchester United and struggled to repeat the heroics of his debut season, when he racked up 27 goals.
The forward has four goals from 15 games for United in all competitions this season and is not certain to lead their attack for today’s visit of Crystal Palace to Old Trafford.
During the international break Mourinho travelled to Belgium to watch Lukaku play in their Nations League tie against Iceland, to try to get to the bottom of the 25-year-old’s goal drought.
Lukaku did not feature for Belgium in that game, and pulled out of their following match, a 5-2 defeat against Switzerland, after feeling tightness in his hamstring.
But Mourinhio opened up on the reason for his trip to Brussels and said he was invited to the game by Belgium boss Roberto Martinez, whose counsel he sought over Lukaku’s ongoing injury and confidence issues.
“I went for the weather,” joked Mourinho. “Beautiful fog, something I don’t have here.
“I went there for, mentally, to be with Lukaku, to feel him, to see his situation and his injury.
“Roberto invited me to meet him, which I decided not to do, because I don’t like people to disturb people before matches.
“But I was with Roberto on the phone, trying to feel, trying to understand the problem and the evolution of the problem and, of course, I like to watch football.
“I was in London within a couple of hours by train, so it was easy to go.’
Mourinho admitted he dropped Lukaku for Manchester United’s 2-1 win over Everton last month because the striker was short of confidence and he wanted to ease the pressure on him.
Lukaku also missed away wins against Bournemouth and Juventus, but came on in United’s 3-1 derby defeat at Manchester City, winning a penalty converted by Anthony Martial.
Mourinho also said he does not believe Alexis Sanchez will leave United in January, despite the forward’s supposed disillusionment at the club after less than a year.
“I don’t think so, because he never told me that he wants to leave or isn’t happy to stay,” said Mourinho. “But I repeat, that is a personal thing related to my philosophy.”
Asked how he felt Sanchez was playing, Mourinho said: “Like the team. He’s improving, like the team is improving, and when he plays he’s giving us his personality, his desire to play and to produce for the team.
“He’s trying to adapt to how we play and vice versa. Can he do better? We can all do better. I can do better, he can do better and all the other players can also do better.”
Mourinho also accused former Real Madrid and Spain keeper Iker Casillas of trying to undermine United keeper David De Gea so he can earn a recall for Spain and add to his record 167 caps.
The United boss was asked how De Gea has been affected by criticism of his form in his native Spain and made it clear he felt Porto keeper Casillas – with whom he fell out at Real Madrid – was behind it.
“Why criticism in Spain? Do you know?” said Mourinho. “I know – because there is somebody very powerful that is thinking about jumping again.
“But it’s very difficult to jump when you have the best goalkeeper in the world in front of you.”