David de Gea, Ander Herrera, Juan Mata and their representatives reportedly feel they are given different treatment compared to the English members of the squad.
Luke Shaw, Phil Jones, Chris Smalling and Ashley Young have all signed new contracts at Old Trafford this season but there has yet to be any similar deal for the Spaniards.
Herrera, 29, is close to joining PSG having failed to reach terms with United and De Gea has one year remaining on his contract and is still a target for long-term admirers Real Madrid, while Mata is also set to depart.