Old Trafford had seemed the most likely destination for the Portugal international, who had been linked with a move to a host of Europe's elite clubs this summer.
United led the chase, while Tottenham also launched a late bid to lure him to the Premier League.
But United were never completely convinced by Fernandes and in the end decided to cull their interest.
It has emerged that United chiefs were left concerned by the midfielder's tendency to give the ball away too frequently.
Fernandes' impressive season saw him plunder 23 goals for Sporting, but closer inspections of his overall play highlighted issues.