The Republic of Ireland midfielder was stretchered off during the 1-1 draw with Bolton in October and is expected to be out until January after undergoing knee surgery.
"During the season a club has very tough periods in terms of lack of numbers, suspensions or injuries, and this is one of them. It is no good feeling sorry for ourselves," Martinez said.
"We have to prepare for a massive game on Saturday against Stoke and look for consistency in our league form."
The Latics are third from bottom in the Premier League and have struggled to find the net this season, with their total of 11 league goals the lowest in the top flight.
Martinez praises Wigan's hard work
But they had scored seven goals in three games against lower division opposition in the earlier rounds of the Carling Cup - and Martinez wants them to pick out the positives from their form in the competition.
"We have to look back at the competition and we played a lot of great football to get into the quarter-final and now we have to take the good things that we did into the league," he said.
"It would be very easy to feel sorry for ourselves, but if we carry on working with levels have been showing, luck can change very quickly."
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