The quartet would have become free agents over the summer and the club has been keen to bolster their transfer values over the next year.
Marouane Fellaini‘s contract also expires at the end of the campaign but admitted himself last month that he was still weighing up his options after rejecting a new deal tabled by the club in September.
But according to the Telegraph‘s James Ducker, Man United have ensured that potential suitors will not be able to sign Mata, Blind, Young or Herrera on a free transfer next summer.
Uncertainty continues to loom over the future of all four players, however, and Jose Mourinho has most likely approved the extensions in order to buy himself time to decide whether any of them fit into his plans for next season.
Mata will likely remain at the club after maintaining his place in the side this season and impressing with some strong performances, while the futures of Herrera and Blind are more tenuous. The former may be kept on if both Michael Carrick and Fellaini depart in the summer, but the Dutchman could fall victim to an overhaul of the full-back position.
Where this leaves Young, who has been one of United’s better players this season but turns 33 in the summer, remains uncertain.