Manchester United boss Jose Mourinho says he travelled to Belgium during the international break to gain insight on Romelu Lukaku.

Mourinho attended Belgium's 2-0 win against Iceland in Brussels on November 15 – and was not watching any of his own players, with neither Lukaku nor Marouane Fellaini involved for the hosts.

Fellaini, who had recently made his return to action after injury, was not part of the squad and has been working on his fitness at United's training ground.

Lukaku sat the game out due to a hamstring problem, and the striker then did not travel with Belgium for Sunday's clash with Switzerland for the same reason.

A post from the striker on Instagram from earlier this week featured videos of him doing exercises, an image of him with Belgium physio Lieven Maesschalck, and a message thanking Move to Cure, a team of injury specialists overseen by Maesschalck.

Lukaku came off the bench in the 3-1 loss to Manchester City on November 11 having been sidelined for United's previous two matches by hamstring trouble.

His scoring record this season shows five goals for Belgium and four for United, and he has not netted in his last 10 appearances for the club.

Mourinho was asked ahead of Saturday's Premier League home clash with Crystal Palace – for which Lukaku has been declared "ready with a little bit of a risk" – about his trip to Belgium.

And after joking that he went "for the weather", he said: "I went...mentally to be with Lukaku, to feel him, to see his situation, his injury.

"Roberto (Martinez, the Belgium manager) invited me to meet him, which I decided not to (do), because I don't like to disturb people before matches.

"But I was with Roberto on the phone trying to feel, trying to understand the problem and evolution of the problem.

"And of course I like to watch football. I was in London, a couple of hours train, easy to go."

While Lukaku and Fellaini are set for involvement on Saturday – along with Paul Pogba, Anthony Martial and Marcus Rashford, over whom there had also been questions marks regarding fitness – Eric Bailly is not.

The defender has not played since being taken off early in the 3-2 win over Newcastle on October 6 when United were 2-0 down.

And Mourinho said: "The situation is that we have five central defenders, and it's a little bit difficult to try to find the best combination.

"I think (Chris) Smalling and (Victor) Lindelof are playing much better than at the beginning of the season. That couple is performing quite well.

"When we decide to make a rotation, we will make (one), when we need to.

"I can tell you, because he already knows, that Eric tomorrow is not playing and is not even on the bench. But don't be surprised that next Tuesday (when United host Young Boys in the Champions League) he plays."

Meanwhile, Mourinho has suggested what has been key to United goalkeeper David De Gea receiving criticism in Spain of late is Iker Casillas expressing his desire to make a comeback with the national team.

Porto goalkeeper Casillas, who won the most recent of his 167 caps in 2016, was quoted by Spanish media last week as saying he would be delighted to return if he received a call-up.

When asked about De Gea, Mourinho – Casillas' boss at Real Madrid from 2010 to 2013 – said: "But why criticism in Spain? Do you know? I know.

"Because there is somebody very powerful that is thinking about jumping (into the team) again – but I think it's very difficult to jump when you have the best goalkeeper in the world in front of you."

Mourinho said the individual used to play for Real and added: "I like him. I was champion with him."

Casillas, who lost his place in the Real team under Mourinho, has been quoted as telling Spain's Vamos he would have confronted the manager over certain things during the three-year spell if he had the chance again, having remained quiet at the time.

Portugal's Record reported being given a response to that by Mourinho, with him saying: "When he says that he has never confronted me, that does not correspond to the truth."