The Honduras defender suffered a groin injury in the Latics' 2-2 draw with Tottenham at the weekend and the initial prognosis was not good.
Martinez has now been forced to concede that Figueroa will miss the last four matches of Wigan's Premier League campaign, as well as the FA Cup final against Manchester City on 11 May.
"We have had real negative news with Maynor Figueroa. He came off in the game really early and the scans have confirmed our worst fears," said Martinez.
"He is going to be out for the rest of the season and probably a longer period.
"He is Mr Reliable, someone who has never missed any sort of time during the time he has been at Wigan Athletic.
"Unfortunately he is now going to miss the most important period in a season."
Martinez also offered an update on other absentees ahead of Saturday's game with Wigan at The Hawthorns and insisted they remain positive about their chances of avoiding relegation.
The Latics trail Newcastle and Aston Villa by five points, although they do have a game in hand on Paul Lambert's side.
Antolin Alcaraz will not face the Baggies but is progressing well as he recovers from a hamstring problem, while Ben Watson could return having been ruled out since November with a broken leg.
Fringe players Fraser Fyvie and Roman Golobart should also add to Martinez's options after overcoming knocks.
"On the other side the positive news is that Antolin Alcaraz is not too far away, but he will probably not be ready for Saturday," he added.
"Fraser Fyvie, Roman Golobart and Ben Watson are also stepping up and they look ready to be involved on Saturday."
"We go into every game fighting for three points and we feel we have to win the game against West Brom.
"It is not something to fear, it is an opportunity and we are all ready to carry on pushing each other.
"Huge respect for West Brom and everything (manager) Steve Clarke has done, they deserve huge credit this season."