The Argentine striker, who has earned senior international recognition with his country this season, struggled to make the grade at Chelsea after arriving in Europe.
A loan spell at Blackburn Rovers allowed him to take in regular first-team football, before completing a permanent move to Wigan in 2010.
Di Santo may not have been prolific during his days at the DW Stadium, but his work rate and willingness to do a job for the team have made him an integral part of the Latics set-up.
Martinez admits as much, saying of his 23-year-old frontman: "He's two different players. The one he was at Chelsea, a young man full of dreams. Now he is a man living his dreams.
"When he arrived at Chelsea, he was a young man with the world at his feet and had to grow up quickly. In football, you need to play games to do that.
"Franco's experience at Chelsea has made him the man he is now. It was an incredible opportunity to come to Europe through Chelsea, but now he's a completely different footballer after the experience he has with Blackburn Rovers and ourselves.
"Franco knows he needed to get away from Chelsea to become his own man, to experience and develop as a footballer. He has come back from Sweden after sharing a dressing room with (Lionel) Messi, Gonzalo Higuain and (Sergio) Aguero. As a striker, that's as nice a dream as you can have in world football.
"Franco needs to progress more and go to another level to improve. He has got the potential to be a vital member of that Argentina squad."
Di Santo's contract at Wigan is due to expire at the end of the season, but Martinez insists preserving the club's Premier League status is of greater importance at present than the future of individual performers.
He added: "In the position we're in, the most important thing is the club. We need to achieve our aim."
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