Ander Herrera has identified Paul Pogba, Anthony Martial and Marcus Rashford as having the potential to become three of the top-five players in world football.
Spanish midfielder Herrera played alongside the trio during his five years at Old Trafford before leaving for Paris Saint-Germain last summer.
United have had a mixed first campaign since the 30-year-old departed, with Pogba, Martial and Rashford each struggling with injuries at various points.
However, Herrera has tipped all three players for a big future if they can show some consistency.
"They have the quality to be among the top 10 in the world," Herrera told The Athletic. "Why do we admire Lionel Messi or Cristiano Ronaldo, or [Eden] Hazard, who I also think is one of the best in the world?
"We admire them because they keep that form for a long time. If they do it, they will become - maybe not Messi or Cristiano, because they are unique in the history of football - but they can be top five or top 10, but they have to do it for a long time and keep it up.
"It is the same for Paul. Rashford is on his way to doing it. And Paul can be the best midfielder in the world if he keeps playing those games where we are all amazed by him. But to keep it at that level is the most difficult thing in football.
"To keep at it it Sunday, Wednesday, Saturday, every time. If those three can do that, Manchester United will win the Premier League soon, for sure."
Speaking in May, Herrera revealed that he had initially hoped to extend his United contract last year.
