Rasmus Hojlund and Joshua Zirkzee have only managed three goals between them in all competitions this season, with the latter netting just once in his first 16 appearances for the 20-time English champions.
Hojliund had a relatively successful first campaign at Old Trafford, scoring 16 times in 43 appearances, but the Denmark international has only managed two goals in 11 outings this term.
Former Man United manager Erik ten Hag had been keen to bring in Harry Kane from Tottenham Hotspur last summer, but the England captain ultimately made the move to Bayern Munich.
Van Nistelrooy was a prolific striker during his time at Old Trafford, netting 150 goals in 219 appearances, and the club's interim head coach has conceded that the lack of a proven goalscorer is currently harming the team.
Hojlund, Zirkzee have only three goals between them in 2024-25
"I agree that when you want to be a successful side in the Premier League and in Europe, and that's what the build is all about, you're going to need a certain amount of goals. That is clear," Van Nistelrooy told reporters when asked whether the club needs a proven goalscorer in order to be successful.
"That is facts in football. And that's why the best teams in the world have those players. At the moment we have players that get a certain amount of goals or assists but they are obviously in an age where they still have to be developed, and there's the potential that they will be, the belief is there that they can. And that's, at this moment, where we are."
Alejandro Garnacho is Man United's leading goalscorer this season with six, while Marcus Rashford and Christian Eriksen both have four, but goals have been an issue in the Premier League this term.
The 20-time English champions have managed just nine in their 10 league matches in 2024-25, with Southampton (seven) and Crystal Palace (eight) the only teams to net fewer at this stage of the campaign.
Could Man United sign a striker next summer? Is Gyokeres an option?
Man United are currently being heavily linked with a move for Sporting Lisbon striker Victor Gyokeres.
There has been speculation surrounding the Sweden international over the last few months, but that has intensified since it was confirmed that Sporting head coach Ruben Amorim would be taking charge of the Red Devils.
Gyokeres has been in incredible form for the Green and Whites this season, scoring 23 goals in 17 appearances in all competitions, while he has 66 goals in 67 matches for his current side in total.
The 26-year-old will allegedly be available for a fee in the region of €76m (£63m) next summer, and Man United are expected to be firmly in the mix for his signature, but Manchester City are also believed to be keen on his services.