Rooney had sympathy for Joshua Zirkzee and Rasmus Hojlund when he analysed their display for his former club in their 1-1 draw to Arsenal on Sunday afternoon. The former England international issued a stark warning to both Arsenal and Manchester United, stating that they won't progress unless they center their squad around a strong number nine.
"I always feel the teams with the best number nines have the best chance of winning things," United's all-time record goalscorer, who won five Premier League titles, told BBC Sport.
"Liverpool are probably an exception to that, with the way they rotate the player they use through the middle, rather than having a regular number nine that the team is built around.
"The number nine is still so important for them, though. Mohamed Salah, cutting in from wide areas, is their main goalscorer but, whether it is Luis Diaz, Diogo Jota or Darwin Nunez in the centre, they all chip in with a good amount of goals."
The Gunners currently have Gabriel Jesus and Kai Havertz out for the season whilst United manager Ruben Amorim is dealing with Rasmus Hojlund and Joshua Zirkzee who have been ridiculed for their lack of goals and underwhelming performances since signing for the club.
Rooney expanded on what he meant by a true number nine and explained that both teams are crying out for a specialist finisher.
"A proper number nine - a forward who has played there his whole life - brings something different to any team," he explained.
"I am talking about that natural goalscoring instinct, which a player who is trying to learn the position probably doesn't have.
"A midfielder playing forward like Merino can get hold of the ball and bring others into play, but what a goalscorer brings is that selfishness of wanting to be in the penalty area to finish chances.
"As we saw on Sunday, Rice was trying to help Arsenal to fill that position, as the player who was always making forward runs and arriving in the box. He did really well in that advanced role, but he cannot always be there."
He defended Hojlund who got a couple of good opportunities to end his drought against Arsenal but failed to find the back of the net which sums up his time at the club so far.
"I've got faith in him. He's a good player who works hard, which is really important. He needs that bit of luck as well, but once he gets a break then more goals will follow.
"As a striker for Manchester United, when you are not scoring goals there is a lot of pressure and a lot of people questioning if you can do it for United.
"When you are short of confidence you have got to make sure you make it into the penalty area and put yourself in a position where you can score, so that is something he can improve on.
"We are still waiting to see Hojlund find his feet for United, but it's important to point out that the whole team have not been at their best. I feel for him from that point of view because, nine times out of 10, forwards rely on their team-mates for service.
"United have not been playing well or creating enough chances, so he has not been in a team dominating possession, sliding balls in behind the defence or putting balls into the box."