Martial moved to Old Trafford from Monaco in 2015 and made an instant impact in his debut season under Louis van Gaal with 11 goals in 31 Premier League games.
The forward, however, has found a starting spot hard to come by with Jose Mourinho on the bench, with 12 of his 30 league appearances in 2017-18 coming off the bench.
And while Martial's agent Philippe Lamboley assures that United are keen to keep him at the club, he feels the time is right for a change.
"After considering all possibilities and options, Anthony wants to leave Manchester United," Lamboley explained to RMC Sport .
"There are many reasons, for now it is too early to discuss it. Anthony will talk soon to go through that.
"Man United want to extend Anthony's deal and they do not want him to leave, but we have not come to an agreement for several months. I think that when Man United, who are the most powerful club, cannot come to an agreement after eight months it is because they really don't want to make him a key player.
"The decision is related to that. It is a decision that has been thought through thoroughly. However, it is important to remember that he is under contract, Man United have the last word and we will respect the club's decision."
While the agent was reluctant to discuss the motivation behind Martial's transfer request, he did hint at frustration at a lack of playing time.
"We do not have the same vision of Anthony's future. Right now Anthony is disappointed because he has shown for three seasons the love he feels for the club and its fans. On top of that, I can tell you that without the fans' unconditional support Anthony would have already asked for a transfer," he added.
"I think he has done his best over the last three years. It is important to remember that this season he scored 11 goals and gave 10 assists in five months. He was chosen Player of the Month three times by fans.
"Where will he play? Right now I don't think that's the most important question. Anthony just wants to play, to feel happy and connect with his coach, that is essential."