With United 1-0 down, Martial blazed their best chance over the bar, prompting Keane to lay into him at the final whistle.
“Martial has come to Man Utd and the big strikers score in the big moments, but his miss [in the second half]sums up his career at Man Utd,” Keane said on Sky Sports.
“Excellent build-up play, but you have to hit the target. No excuses.”
He added: “The big strikers who are remembered by the supporters hit the target and the back of the net, and that’s why that guy [Martial] is not quite good enough for Man Utd. That moment summed him up.”