The 21-year-old striker was given his chance to shine in last weekend's FA Cup fifth-round clash with Huddersfield and took it, scoring in Wigan's 4-1 win and demonstrating his potential with a fine all-round performance.
The cup has provided some much-needed cheer for Martinez's side, who have not won in the league since December and have slipped three points adrift of safety ahead of Saturday's crunch clash with fellow strugglers Reading at the Madejski Stadium.
And the Spaniard believes the performances of fringe players like McManaman are just as important as results in ensuring their league form receives a boost.
He said: "What's important in those situations is that the competition for places is really strong.
"You do feel you get a real boost internally, you get a couple of players back from injury, you get a very good performance away from home allowing you to progress in the cup and now you can focus on a very, very important league game.
"It's vitally important that we have as many players available to compete for their places from now until the end of the season.
"I think we've been a little bit light in the last few months in terms of numbers and options and then all of a sudden now we're quite strong. I think we'll be stronger for the final third of the season, which is crucial for us."
McManaman has been given a smattering of opportunities since making his Wigan debut at the end of the 2008/09 season as an 18-year-old.
He scored his first goal for the club in an FA Cup tie in 2011 and also made a good impression in a loan spell with Blackpool in the Championship last season.
His Premier League chances have been limited to substitute appearances so far and he is yet to score a goal, but Martinez could not be happier with the 21-year-old.
"Callum is a real example of what we want in our football club - youngsters that, if they work well, if they apply themselves well, are going to have opportunities," said the Latics boss.
"Callum has been doing that. He's been working really hard and enjoying his football, and what he did on Saturday is going to help him a lot but more importantly it's going to help the team because that talent is welcome in any group of players.
"We're delighted that Callum is developing into an impressive young footballer and he's going to be very important for us until the end of the season."
Martinez did not tell McManaman he would be playing against Huddersfield until the day of the game to ensure he did not get too nervous, and it is not inconceivable he could be given another start against Reading.
Martinez said: "He's a player who can create something out of nothing, and those players are quite rare.
"We need to understand he is still a young man and he's still developing, and he deserves that time and that patience to allow him to be as good as he can be.
"But clearly this season he's put himself in a position where, as you saw in the last game, he can be effective. He's got very strong football concepts, which for a young player is very important.
"Starting or not starting is not the big question, it's whether he's ready to help the team. And the answer is yes."
Wigan's cause has certainly not been helped by a succession of injuries, particularly to defenders, but Saturday could see the long-awaited return of Antolin Alcaraz.
The centre-back last played for the Latics in August before tearing a groin muscle on international duty with Paraguay but has been training with his team-mates and could make the trip to the Madejski Stadium.
"Antolin has been very positive," said Martinez. "He's been working with the group so I don't think he's going to be too far away. He was very close to making it in the FA Cup game and finally I didn't think it was right to risk him.
"He's fully fit now it's just that he hasn't played since September, and to get that match fitness is important. I think he's got a good chance to be in the squad on Saturday."