The striker, 27, joined Fulham on a free in the summer and returns to the DW Stadium today.
Latics boss Martinez said: "Hugo made his mind up a long time ago that he wanted to respect his contract but then move on. He needed a new challenge.
"We have a very good relationship with Hugo. You have to respect the human being behind the footballer.
"And it was right for him to start a new chapter.
"We've brought in new players and we have new aims now. We've made progress off the field."