Lukaku has gone eight matches without finding the back of the net with his performances in those games also disappointing.
United host Lukaku’s former team Everton in the last game of the Premier League on Sunday.
Jose Mourinho however believes it will not be long before his striker enjoys a good streak in front of goal.
“I think one of the best scorers in football had funny words about it. It was when Cristiano Ronaldo was speaking about the ketchup bottle and when you [shake it]. The goals are coming and coming and coming,” the Portuguese told Sky Sports.
“I believe with Lukaku that this will happen, but the reality is that in this moment it’s not happening.
Mourinho recognizes the fact that is not just the goals that have been missing in Belgian’s game recently.
“There’s been lots of matches in which he’s not scored a goal, and not just scoring but also the performances, the happiness in the performances, I think is the problem.
“But he’s a good player. A good boy, and I think the best way to do it is to just keep working and the moment will arrive.”