Antonio Valencia and Lee Cattermole were the only high-profile exits from the DW Stadium, and Martinez is convinced he has a squad strong enough to compete in the Premier League.
He told the club's official website: "You always need to look to help the squad you have.
"I'm not the sort of person to just bring in players for the sake of it, Wigan Athletic doesn't work like that.
"In that respect I'm delighted with the squad I have here and now we need to work hard and achieve our potential as soon as we can.
"One of the most important things for us was to keep hold of our key players, those who have been attracting interest from elsewhere."