Martial scored the only goal in the 1-0 win over Burnley on Saturday.
And he has been in form in recent weeks with three goals in his last four games.
United are closing in on Sanchez, who has gone to sort out the paper work for his move to Old Trafford, putting Martial’s place in the team in doubt.
But Matic reckons the young France star can keep showing his best.
“Anthony is a great player as you know and he scored an important goal today,” he said following United’s narrow win.
“He is very important for our club, our team. He’s still young and can still improve . I’m sure he with help us a lot.”
Sanchez played mainly on the left for Arsenal and is expected to go straight into the United side with him becoming the highest-paid player at the club.
But the big question for Jose Mourinho is where to fit in his new No 7.
The Sanchez deal is expected to be announced this afternoon with the work permits being sorted out now for both Sanchez and Henrikh Mkhitaryan, who is joining Arsenal in return.
Both players are expected to be unveiled today and could make their debuts in the coming days.
Sanchez will be expected to slot straight in against Yeovil while Mkhitaryan will play against Swansea next week after missing the League Cup match this week because he’s cup tied.