Lukaku has scored 10 goals in nine appearances since joining from Everton for an initial £75m in the summer transfer window.
The 24-year-old continued his hot streak with a brace in last night’s thrashing of CSKA Moscow.
“They are amazing numbers for Romelu,” Mourinho told the press after the Champions League win.
“He is humble and wants to learn and improve all the time.
“I think ambition is there and I trust he can keep performing for us.”
Mourinho, however, was keen to stress that Lukaku’s excellent start has been made possible by his team-mates.
“It is a great achievement but it is only possible with a good team,” the United boss added.
“Without a good team it is not possible and the team is playing well.”
United are unbeaten in nine games since losing the UEFA Super Cup to Real Madrid last month.
Anthony Martial and Henrikh Mkhitaryan were also on target against CSKA.
The win leaves United top of Group A.
