The £20million man will make his debut against Sheffield United on Monday after joining from Arsenal this week.
He penned a four-year deal at Villa Park and the club moved for him with Tom Heaton yet to return from a serious knee injury.
But despite the price tag boss Dean Smith insisted Martinez has to earn his spot.
He told a press conference: "He's ready to play, whether he's our automatic number one depends on what he does in training and matches. He played against us a couple of weeks ago for Arsenal, so we know he's ready to play.
"He's played In the Community Shield as well, so he's probably had more games than our goalkeepers so far. In terms of readiness, he's 100 per cent.
"He has to go and earn the shirt – all the players know that. You don't get many opportunities to get a goalkeeper of his calibre at this stage of his career."
Heaton is not expected to be available for at least a month while striker Wesley remains out with his own long-term knee injury.
Villa finished 17th, beating the drop by a point last season, and Smith is determined to avoid another close call.
"We're looking at improving and we weren't satisfied with finishing 17th in the league," he said.
"We believe, with the players that we've got, that we'll be better for our experiences last season.
"We stayed up on the last day last season and we learnt a lot of lessons. We had a lot of change from the previous season and a lot of injuries as well.
"Hopefully we don't have those injuries this year and we can be a better team than we were. Our aim now is to finish higher than we did last season."