The Dutch manager has toyed with various options within the current squad in an attempt to rectify the problem, including playing Rooney in midfield.
“Signing a creative player should be our priority this summer,” the 63-year-old said. “I’m looking for balance and I need it in midfield.
“In the last few games I’ve played Adnan Januzaj and Angel di Maria in the midfield positions, and you need a certain balance for that kind of creative player.
“Radamel Falcao and Robin van Persie are also creative players so then you have four of them, and you still have to look for balance in your team.
“Wayne is playing in midfield because there is no one else. He’s happy to do so otherwise he should come to me and say he’s not, but he never does. He’s always friendly to me and wants to perform.
“But of course when the whole world is writing that he has to be in the striker’s position then he will be thinking ‘hey, maybe’. He’s human.”