Manchester United must ensure they do not sign players who are only "coming for the money", Rafael says.
United have invested huge sums in the playing squad since Alex Ferguson retired in 2013, yet they have failed to get close to winning the Premier League in that time.
A lack of clear direction from a director of football figure and four changes in permanent manager have left United's transfer policy mostly disorganised, with significant money in fees and wages spent unsuccessfully on the likes of Angel Di Maria and Alexis Sanchez.
Under Ole Gunnar Solskjaer, the club's transfer approach has shown marked improvement, with the former United striker making it clear he will only sign players who possess the right ethos as well as suitable talent.
The arrivals of Daniel James, Aaron Wan-Bissaka, Harry Maguire and Bruno Fernandes in the past year have all proved to be positive, with Solskjaer ensuring youngsters from the academy system are still given the opportunity to play alongside expensive signings.
Despite concerns around the viability of the market during the coronavirus crisis, United have been tipped to try to sign Borussia Dortmund star Jadon Sancho and Tottenham striker Harry Kane this year.
Rafael, a three-time Premier League champion with United, is a fan of both players but nonetheless wants his former employers to be sure they sign only those who want to move to Old Trafford for the right reasons.
"It has taken too long to get back on track," the Lyon 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 says. "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."
United have been well off the pace set by Premier League leaders Liverpool this season, but Rafael is in no doubt that Solskjaer is the right man to lead his old club forward.
"I love Ole. I love the person he is and the manager he is," he said. "Of course, there is a lot still to do but I think he's doing it the right way. He's a person who loves Manchester United and he's going to do everything to help the club. I saw it when I was with him when he coached me and it is important.
"He's a guy who is going to think about Manchester United first rather than himself. A lot of coaches are never going to do that, they are going to think about them and after about the club."