However, significant investment in January could convince Rooney that United will be serious contenders for the next few years.
Below are three players who would push the Red Devils back up the table and ensure Rooney commits his future to the club.
Arturo Vidal, Juventus
It's a long shot—and Juventus would try to squeeze every penny out of the deal—but a player of Arturo Vidal's quality would immediately upgrade the team and see them challenge for the title once more.
United have been clamouring for a quality midfielder—as evidenced by the disastrous lunge for Marouane Fellaini in the summer—and Vidal is one of the best in the world right now.
The Mirror reported that David Moyes is ready to "break the bank" to ensure that Vidal arrives in Manchester and a huge rise in wages may do just that.
However, Vidal only signed a new Juventus deal in December and it remains a massive task to prise him away from Turin.
If Moyes was to pull this off, it would be a remarkable coup and demonstrate to the world—and Rooney—that United retain the buying power they boasted under Sir Alex Ferguson.
Koke, Atletico Madrid
The rumours surrounding Manchester United and Atletico Madrid's Koke just won't go away, and Moyes would be correct to pursue the 21-year-old.
A recent report by Goal.com stated that Moyes has sent his delegates to Spain to negotiate a deal with Atleti, which would be a strong statement of intent by the United boss.
Once again, however, it's going to take a lot to secure the player's signature.
Koke recently signed a deal that commits him to Atleti until 2018, which would mean a significant outlay to make him a United player.
Atletico are currently enjoying a season that has seen them emerge as strong contenders in La Liga, putting in excellent performances against both Barcelona and Real Madrid. Champions League football is in the club's future, while United can make no such guarantees right now.
The World Cup also remains in the eyes of players weighing up a January move, and Koke will be hoping his current form forces him into the Spanish national set-up.
A move to Old Trafford could see him well-rewarded financially, but any sort of drop in form could see him miss out on playing time in the World Cup.
Marco Reus, Borussia Dortmund
Marco Reus recently spoke out about his commitment to Dortmund, but it wasn't particularly emphatic. ESPN quoted the midfielder as saying: "I have got a valid contract at Dortmund and I am happy to be here."
Note that he never said that he would reject any bids for him, just that he is happy to play for his current side. That doesn't fully close the door, so a deal for Reus remains one worth keeping an eye on.
It had previously been reported in the Daily Mail that the German would cost Moyes up to £40 million, which would be an expensive purchase. Nevertheless, Reus would provide the creativity that United lack and link with Rooney to create an attack to be feared.
Moyes will be reluctant to overpay, considering the reaction to the Fellaini transfer, but if he is truly committed to signing the world's best, he'll have to pry them from Champions League clubs demanding big money.
It would certainly demonstrate a willingness to bring in top talent, but Moyes will not want to be hamstrung by a huge asking price that may not reflect a player's true value.