Rafael, who currently plays for French Ligue 1 side Olympique Lyon, won three Premier League titles during his time as a Manchester United player.
The 29-year-old Brazilian was a member of the last Red Devils side to win the Premier League in Sir Alex Ferguson’s final season as Manchester United manager in 2013.
In a bid to get back to the top, United have splashed the cash on a number of high profile signings in recent seasons that ultimately failed produce the needed results at Old Trafford.
The likes of Angel di Maria, Alexis Sanchez, Radamel Falcao, Romelu Lukaku and Henrikh Mkhitaryan all arrived on fat paychecks but failed to live up to expectation.
The appointment of Ole Gunnar Solskjaer as manager has seen United focus on young, hungry players to complement the experienced ones and they have been linked with the likes of Jadon Sancho and Harry Kane in the next transfer window.
However, Rafael wants his former side to be cautious in their dealings and bring in players who are ready to die for the club.
"It has taken too long to get back on track," the full-back told ESPN.
"It's been seven years [without the title]. We did some things wrong. We started signing expensive players and giving them a lot of money. I don't agree with that. Just because a player costs 150million does not mean he's good for the team. It depends on the character of the player.
"They should go for the players who want to play for Manchester United, not just because Manchester United are going to pay you. Look at Chicharito [Javier Hernandez]. How hard did he play for Manchester United? He wanted to play. How much did Manchester United pay for him? Not much. You have to be clever. You have to see that the player wants to play for Manchester United.
"Harry Kane is a great goalscorer and Jadon Sancho is very, very good," he added. "But first of all you have to see the character of the player and see if they really want to do well for United, not just coming for the money. We have made some mistakes, but I hope now that we can get back on track. In this Manchester United, I see more of how they played before and I think soon we will be back where we belong."
