The young striker has impressed the former Arsenal and England defender since his big money move from Monaco.
Though many people questioned the size of the transfer fee associated with the France international's move from Monaco, with various sources such as the BBC suggesting it was £36 million and possibly rising to £58 million, the former England star lauded the 19-year-old, claiming he had been sensational in his few appearance so far.
"He's been absolutely magnificent. They could not have hoped for any more," Keown told Match of the Day 3 at the weekend.
"There was a huge transfer fee on his head, but it doesn't seem to bother him. Every time he is in front of goal he seems to be at his happiest.
"He looks very powerful and mature and he's well beyond the age he played at on Sunday."
Martial added to his sensational debut goal against Liverpool by scoring a brace against Southampton in United's 3-2 win at St Mary's at the weekend.
The forward scored nine goals in the league for Monaco last season, and he has already managed a third of that total in two Premier League matches.
With the youngster also winning his first international caps this month, it looks like being a breakthrough season for the promising striker, and if he can continue to look as dangerous in front of goal as he has done so far, there will be many more people celebrating his signing in the future.