United boss Sir Alex Ferguson believed Ben - now 23 - had an "outstanding" chance of stardom.
Playing in his first reserve game and on the verge of being offered a three-year contract, his leg was broken in two places by Middlesbrough's Gary Smith.
Both Smith and Middlesbrough FC admitted liability for the "negligent" tackle through their insurers and a High Court judge awarded Ben the £4.3million.
The figure could rise to £4.5million when sums for future loss of pension and interest on past loss of earnings are added.
In a statement after the hearing in London, his solicitor Jan Levinson said: "Ben and his family are happy that this case has finally come to a close and that Ben is now able to move on to the next chapter.
"The size of the award made by the court reflects his talent and potential as one of the brightest young footballers in the country.
"Having said that, Ben would have preferred to earn this sum through a full career as a professional footballer.
The judgment is the highest award ever given to a professional sportsman or sportswoman."