France forward Martial won the penalty from which Bruno Fernandes scored to send United to the semi-finals via a 1-0 extra-time win in Cologne on Monday.
The Red Devils had 14 shots on target and hit the woodwork twice in the quarter-final tie against the Danish outfit, with Martial impressing while leading the line ahead of Marcus Rashford, Fernandes and Mason Greenwood.
Former United midfielder Hargreaves was effusive in his praise when commenting on Martial's fine performance as part of his role as a pundit for BT Sport.
"Everyone's got an opinion on Martial. He's a Ferrari," he said.
"He just looked like a £100 million player."
His performance also drew applause from manager Ole Gunnar Solskjaer, who has been impressed by the 24-year-old striker's development over the course of the season.
"He was sharp," the Norwegian coach told reporters.
"Anthony has developed throughout the season, he was involved with the penalty.
"He's impossible to stop at times when he gets the ball into his feet and he drives at people, his balance, he can go either way.
"The only thing now is to put that ball in the back of the net again. I'm delighted with his performance, though."
Ex-United forward Robin van Persie was also impressed by what he saw and described Martial as "world-class", while club legend Paul Scholes hailed him as “unstoppable”, adding: "Now I think he’s brought the all-round game. He’s got everything, he can beat a man, he can score goals, he’s got everything you’d want in a centre-forward."
Martial has scored 23 times in 47 appearances in all competitions this season, making him United's top scorer in 2019-20, with Rashford one goal behind.
United, who are chasing their first piece of silverware since 2017, will face the winner of Tuesday evening's tie between Wolves and Sevilla in the final four of the competition, while Shakhtar Donetsk and Basel will square off to decide who will take on Inter in the other semi-final.