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."
