With Pogba reportedly earning upwards of €15m a year, Madrid would be reluctant disrupt the current salary hierarchy at the club.
Not only are wages a probable stumbling block, but United would take some convincing to sell a player Ole Gunnar Solskjaer has previously stated he should be building a team around.
Pogba's agent, Mino Raiola, will also play a significant role in any transfer, though the Dutchman doesn't have the best relationship with either club.
Zidane is expected to have a considerable transfer budget to overhaul Madrid's squad this summer, with Pogba a priority target.
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