There are some of you so eager to blame Martial but looking at this situation objectively or through the eyes of Martial its absolutely evident Jose will never fully trust him.
July 2016 - Martial loses his number 9 shirt to Zlatan without being consulted. Immediate loss of trust from a manager he's yet to meet
November 2016 - Having been our best outfield player in 2015/16, Jose Mourinho admits the following regarding Martial;
"First of all the teams are very different. The way the team played last season – I’m not saying better or worse, just different – was probably more adaptive to Anthony. He was probably more comfortable playing that way, at that intensity, at that [rate] of ball possession and ball circulation. You have one opportunity, you have two, you have three – if you don’t bite, then somebody comes and takes the bait.”
December 2016 - Jose tells Martial "Listen to me and not your agent, I improve player". He cited Mkhitaryan as an example of someone who was willing to listen in order to improve. A year later Mkhi is marginalised and sold.
April 2017 - Says Martial "has to give him things he likes", he even uses Rashford as a shining example despite him having not scored since September. These things clearly aren't scoring goals but intensity and tracking back opposing fullbacks.
2017/18 - To begin the season, Martial is again resigned to the bench but after stellar displays off the bench, he forces his way into the starting 11 rotation with Rashford. Some very good and some average performances followed, however his productivity was among the highest in the league. After clearly outperforming Rashford in November and December, Jose still opts to alternate their starts with Rashford being the preferred choice for PL games. Jose finally gives Martial the starting berth in January and Martial is our player of the month. Excellent goals in wins against Everton, Burnley and Stoke. Just as he's ready to kick on, Sanchez is signed and pretty much takes his spot immediately in our team.
After the signing of Sanchez, Martial's minutes have reduced. Lukaku and Sanchez are untouchable, meaning he's fighting for 1 spot with Rashford and Lingard with the latter being the preferred option. There is nothing Jose has done in his reign to assure Tony of his trust so to lay the blame on him is disingenuous and ignoring the facts.
If I were his agent or his parent I'd be advising him to leave as most of you would too.