Oviedo suffered a bad break to his left leg in Everton's FA Cup fourth round win at Stevenage in January, and the 24-year-old looked certain to miss the finals in Brazil later this year.
However on Thursday, Martinez revealed that Oviedo's rehabilitation was going better than expected and that he may yet make a remarkable recovery in time to be a part of Costa Rica's plans.
"He is really well and back in Costa Rica now," he said.
"He's working with the national team and we've got high hopes that he'll be able to be fully fit for the World Cup.
"In that respect it's a nice target to hope for and he's been well ahead of the timing that we were expecting.
"We're hopeful in that respect because no-one deserves it more than him to have a chance to play in the World Cup."
Oviedo made his Costa Rica debut against Argentina in 2010 and has 26 caps to his name.
