That is according to former Manchester United and England midfielder Ray Wilkins.
Romelu Lukaku has been United’s main centre-forward so far this season and scored 11 goals in his first 10 games for the club since joining from Everton in the summer.
However, the Belgian is currently on a goalless run of seven matches in all competitions, leading to criticism from some supporters.
Meanwhile, Zlatan Ibrahimovic is set to return to action following his knee injury by the end of the year.
Wilkins believes the the Swede can have an impact on the destination of the title, with United currently eight points behind Manchester City at the top, as well as Paul Pogba.
And he says Mourinho must soon decide who he will put his faith in up top.
“They (City) look phenomenal at the moment but I would say when (Paul) Pogba comes back, it will make a huge difference,” Wilkins told talKSPORT.
“But also coming up to Christmas, you’ve got the monster coming back as well. Zlatan Ibrahimovic.
“He will be coming back and he will have such an influence on this Manchester United side, it’s incredible. I really do believe that.
“Cruciates now are like cartilages 50 years ago.
“I do believe when Ibrahimovic comes back, it’s going to test Lukaku for a start.
“Does Lukaku play or does Ibrahimovic play? Jose Mourinho has to make a massive decision.”
Published at Wed, 08 Nov 2017 18:39:56 +0000