The Swede has signed to the end of this term and has returned to training this week after recovering from April knee surgery.
However, Mourinho is already drawing up plans to replace Ibrahimovic with Tottenham star Harry Kane.
“The problem for United is the money could get to a ridiculous level. It's going to be more than Kylian Mbappe.
“It's money they can lay their hands on but it will be interesting to see what Levy's stance on the whole thing will be."