The current Chelsea star is set to complete a move to the Red Devils in a deal worth £60million.
The move will bring an end to his 18-year stay with the Blues where he gained promotion from the club's academy into the first-team.
Mount is on the verge of being United's first signing of the summer as Erik ten Hag looks to build on an impressive debut season.
With a move close to completion, fans have been reminded of a previous clash between Mount and star defender Martinez.
Chelsea hosted United in a dramatic 1-1 draw in October that saw Casemiro's stoppage-time goal cancel out Jorginho's late penalty.
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Earlier in the match, Mount and Martinez were tussling for the ball and the former was adjudged to have fouled the latter.
The United centre-back then gave the Chelsea man a push in the chest before the duo came face-to-face.
Luke Shaw was quick to intervene and separate the two, but fans think there could soon be an awkward reunion.
On Twitter, one said: "They'll spend the first day squaring it out!"
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"Can't wait to see Licha get him again," added another.
However, one fan remains optimistic that they can put aside their past differences: "They are teammates now. If anything they will respect the fight in each other."
With Old Trafford beckoning, Mount will be the latest star to depart Chelsea this summer.
He will follow N'Golo Kante, Kalidou Koulibaly, Mateo Kovacic, Edouard Mendy, Kai Havertz and Ruben Loftus-Cheek out the door in a huge squad overhaul at Stamford Bridge.