Owen Hargreaves feels Manchester United need to take a leaf from their rivals' transfer book if they want to take the "next step" in their evolution.
United built on the progress of last season to finish second in the Premier League, giving them plenty of optimism for a full title challenge next term.
With the prospect of a first trophy under Ole Gunnar Solskjaer also on the table, it could be a successful end to a decent campaign for the Red Devils.
But thoughts have already begun turning towards the summer and players United could bring in to help boost their chances.
And Hargreaves has urged his old club to look no further than the two stars who transformed both Liverpool and Man City, and find their own version.
"United could win the Europa League but the goal is to win the Premier League and the Champions League and to do that they need investment, the right recruitment, key players in certain positions," Hargreaves told Goal.
"So for United to compete they’re going to have to invest heavily and back Ole, because Ole has got them in a position where they’re within striking distance and I think that’s good. A lot of teams sign good players but they’re not difference-makers.
"I like [Victor] Lindelof, I think he’s a really good player, but I think you’ve seen the impact [Ruben] Dias has had at Man City and the impact [Virgil] Van Dijk had [at Liverpool] and it might take getting one of those guys in to help Man Utd take the next step."
Central defence has remained a problem area for United, even after shelling out £80million on Harry Maguire two years ago.
And Hargreaves' comments may cause United chiefs to rue the mistake made by executive vice-chairman Ed Woodward in the same window, to pass up the chance to sign the aforementioned Dias.
As was reported, Dias was one of several options on United's shortlist as handpicked by ex-boss Jose Mourinho.
But the Portuguese defender was overlooked due to his age (21 at the time), as United wanted to land a more proven option.
That decision has now come back to bite them as Dias has flourished for their rivals while United still have limitations due to their centre-back pairing.
Real Madrid's Raphael Varane, Sevilla's Jules Kounde and Villarreal's Pau Torres have all been linked with a switch to Old Trafford this summer, but all would face a big task to replicate Dias' impact over at the Etihad.
