Roberto Martinez believes defensive injuries caught up with his Wigan side in a 3-2 defeat by Swansea that leaves them three points adrift of safety.
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Antolin Alcaraz missed the game while Ivan Ramis and Maynor Figueroa have been ruled out for the season.
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Ronnie Stam, who made his comeback as a substitute against the Swans, injured his leg in the Latics' latest defeat.
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"The many injuries we have at the back showed, we played sloppy balls and made bad decisions," said Martinez.
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"Defensively we are so lacking with bodies and important players, that has a massive say - keeping clean sheets is always important."
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Swansea's winning goal came after Shaun Maloney and James McArthur failed to clear Pablo Hernandez's cross, allowing Dwight Tiendalli to stab home.
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In the Latics' previous home match a mix-up between goalkeeper Joel Robles and Figueroa had allowed Gareth Bale to open the scoring in a 2-2 draw with Tottenham.
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Although Alcaraz is likely to return before the end of the season, Stam looks set to sit out his side's remaining Premier League matches away to Arsenal and at home to Aston Villa as well as Saturday's FA Cup final against Manchester City.
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"We will check Ronnie [on Wednesday], but it seems it is a broken leg," said Martinez.
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"He couldn't put any weight on it, so he will need a scan to find out exactly what it is."
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Martinez also said that it would be "difficult" for Jean Beausejour, who injured his hamstring in Saturday's 3-2 win over West Brom, to return before the end of the season.
They've been very poor in the English Premier League. The coach has to do more to motivate them when it comes to league games.