Del Bosque, 63, was not interested in listening to the personal terms on offer, according to AS, despite Sir Alex Ferguson endorsing United's proposal. United installed Louis van Gaal as manager last week.
The former Real Madrid coach also rejected the opportunity to take over at Internazionale, despite a personal plea from one of his former players, and Inter ambassador, Luís Figo.
Regarded as one of the game's greatest coaches this century, Del Bosque, whose contract with La Roja runs until the 2016 European Championship, managed Spain to their 2010 World Cup and 2012 European Championship triumphs.
And in three-and-a-half years managing Real Madrid at the beginning of the century, he delivered two La Liga titles and two Champions Leagues.
Del Bosque has only managed abroad outside of Spain at Turkish club Beşiktaş, where he lasted less than a season.