French forward Martial became the most expensive teenager in history at the time when he completed a September 2015 move worth up to £58million (€69m) from Monaco.
Signed by Louis van Gaal, he spent less than a year playing under the Dutchman, with whom he said he had “a great relationship”.
Mourinho was Van Gaal’s successor, appointed in May 2016, and Zlatan Ibrahimovic was among the first signings by the new boss.
According to Martial, his problems with Mourinho “started with the story of the jersey number”, saying he unwillingly gave up the number nine to Swedish star Ibrahimovic.
“During the holidays, he [Mourinho] sends me a message to ask me if I want to change to the 11, explaining to me that it is great because it is that of the legend Ryan Giggs,” Martial told France Football magazine.
“I tell him that I have the greatest respect for Giggs, but I prefer to keep the nine. And when I return to the club, I see my jersey with the 11, the story didn’t start well. He lacked direct respect for me.”
Martial said Mourinho, who is now boss of Roma, began to use “little phrases, a bit like he had done with Karim Benzema at Real [Madrid]”, when talking in the media about Martial.
“He likes these little games, but he also knows who he is doing it with. He knows that I was 20 years old then, and that if I say something it is me who will pass for the young person who lacks respect,” Martial said. “So I said nothing, it was useless.”
Martial took issue with losing his place to another new recruit, Alexis Sanchez, who joined from Arsenal midway through the 2017-18 season.
“It’s the season of the World Cup, and it cost me dearly in the end, especially since the France team won. I should have been there,” Martial said.
Mourinho was sacked by United in December 2018, with club favourite Solskjaer coming in as a surprise successor.
France international Martial finished the 2019-20 campaign as United’s top scorer with 23 goals, yet he subsequently faded from favour. He claimed Solskjaer mismanaged him after that prolific campaign.
Soon after Solskjaer’s dismissal in November 2021, Martial was loaned out to Sevilla, where he scored once in 12 appearances, nine of which were starts.
Martial said he had “regularly played injured” during Solskjaer’s reign, claiming the manager failed to make that clear to outsiders as he struggled.
“The coach never bothered to tell the media,” said Martial, who remains a United player. “Obviously, I ended up getting injured for good and when I came back I didn’t play any more. I took it very badly, I had a feeling of injustice.
“You’re asked to sacrifice yourself for the team and afterwards you are dismissed. For me, it’s almost treachery.”