Martinez also compared the Inter Milan striker with legendary Argentine forward Diego Maradona.
The 26-year-old enjoyed a mixed spell at United scoring an impressive 42 goals across two seasons before he left to join Inter Milan last summer.
Speaking about the Inter forward Martinez questioned the attitudes towards Lukaku and compared his coverage to that of football legend Maradona.
“Yes, yes, I am surprised,” he told The Times.
“Pundits have this knack of always highlighting what a player hasn’t got or doesn’t do. There are certain players we always highlight the good things they do, and for other players there are things we highlight they don’t do. Rom fell into that category after his time at Chelsea.
“He had a phenomenal couple of seasons at Everton, but the moment he left Everton [for Manchester United] there was almost that feeling that everyone was going to highlight when Rom didn’t score, then it would be a negative about his performance.
“That’s been surprising for me because Rom has outstanding qualities. He’s a goalscorer, he cannot be measured about the other things he doesn’t do, like Diego Maradona ‘couldn’t tackle’, ‘couldn’t be good in defensive set plays’ or ‘couldn’t use his right foot’. Nobody would speak how many times Maradona used his right foot. Rom is a goalscorer. That’s his job, and what he does best.”
Lukaku is already the top scorer in the history of the Belgian national team and helped guide the team to a third-place finish at the World Cup in 2018.