Manchester United, if we want to be competing with the best, need to have great players. I believe Martial can be a great player, he has the ability but lacks some consistency. Look at Real Madrid or Barcelona.
At Madrid they have: Ronaldo, Benzema, Bale, and Isco... but backing that up they have Asensio & Lucas.
At Barca they have: Messi, Suarez, Coutinho, and Iniesta... but they've also signed Dembele for massive money, who has huge talent.
Nobody would be surprised if there was an El Classico where Dembele and Asensio didn't start. Martial, for me, should be compared with these players, not with Ronaldo and Messi, or Suarez and Bale for that matter.
We have: Lukaku, Sanchez, Mata, and Lingard... backed up by the young, but exciting Rashford and Martial. Ibrahimovic has moved on.
Real have fallen short this season because although Ronaldo's goal return is still excellent, for one reason or another, Benzema & Bale have failed to live up to their billing.
Asensio and Isco have been brilliant in games, but inconsistent.
We've fallen short because although Lukaku has been scoring well, Ibrahimovic missed the season through injury; Sanchez has just joined, and is taking time to get up to speed; and although Mata has given our team balance and control, he has been inconsistent in his effectiveness at breaking teams down this season.
We're doing ok, but for me, it's more likely to be Mata at risk rather than Martial.